Photocurable ink composition, recording method, recording apparatus, photocurable ink jet recording ink composition, and ink jet recording method

ABSTRACT

A photocurable ink composition includes polymerizable compounds and a photopolymerization initiator. The polymerizable compounds include vinyl ether group-containing (meth)acrylic esters represented by the following Formula (I):
 
CH 2 ═CR 1 —COOR 2 —O—CH═CH—R 3   (I)
 
(wherein, R 1  represents a hydrogen atom or a methyl group; R 2  represents a divalent organic residue having 2 to 20 carbon atoms; and R 3  represents a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms), dipropylene glycol di(meth)acrylate, and monofunctional (meth)acrylate having an aromatic ring skeleton. The ink composition includes a coloring material.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matters related to JapanesePatent Application No. 2011-101154 filed in the Japanese Patent Officeon Apr. 28, 2011, Japanese Patent Application No. 2011-248281 filed inthe Japanese Patent Office on Nov. 14, 2011, and Japanese PatentApplication No. 2011-127326 filed in the Japanese Patent Office on Jun.7, 2011, the entire contents of which are incorporated herein byreference.

BACKGROUND

1. Technical Field

The present invention relates to a photocurable ink composition, arecording method, and a recording apparatus. The invention also relatesto a photocurable ink jet recording ink composition and an ink jetrecording method.

2. Related Art

Various systems have been utilized as recording methods of formingimages on recording media such as paper based on image data signals.Among them, an ink jet system is an inexpensive apparatus and directlyforms an image on a recording medium by discharging an ink only on anecessary image area and therefore efficiently uses inks at low runningcost. In addition, the ink jet system is low in noise and is thereforeexcellent as a recording method.

Recently, in the recording method of the ink jet system, a photocurableink composition, which is cured by light irradiation, is used as an inkcomposition that can provide high water resistance, solvent resistance,abrasion resistance, etc.

For example, JP-T-2004-526820 discloses an ink jet ink that does notsubstantially contain water and/or any volatile solvent and contains atleast one multifunctional (meth)acrylate monomer, at least oneα,β-unsaturated ether monomer, at least one radical photopolymerizationinitiator, and at least one dispersible pigment. The content of themultifunctional (meth)acrylate monomer is 2 to 15 parts by weight basedon 1 part by weight of the α,β-unsaturated ether monomer, the ink has aviscosity at 25° C. of less than 100 mPa·s, and the content of theα,β-unsaturated ether monomer in the ink is 1 to 30% by weight.

For example, JP-A-2008-19292 discloses a photocurable composition thatcontains a polymerizable compound (a), 0.1 to 15% by mass of aphotopolymerization initiator and/or photoacid generator (b), and 0.001to 5% by mass of at least one of fluorochemical surfactants, siliconesurfactants, and fluoro-silicone surfactants (c), and has a viscosity at25° C. of 3 to 18 mPa·s (d). The polymerizable compound (a) includes apolymerizable unsaturated monomer (e) having a primary skin irritationindex (PII) value of 4.0 or less and a polymerizable unsaturated monomer(f) having a viscosity at 25° C. of 30 mPa·s or less each in an amountof 50% by mass or more. The polymerizable unsaturated monomer (e) andthe polymerizable unsaturated monomer (f) may be partially or totallythe same polymerizable unsaturated monomer.

For example, JP-A-2004-224841 discloses an active energy ray-curablecomposition containing prescribed vinyl ether group-containing(meth)acrylic esters (A), a 1,3-dioxolane ring and/or2-oxo-1,3-dioxolane ring (B), and a photopolymerization initiator (C).

For example, JP-A-2008-179136 discloses a method of forming an image byapplying an undercoating liquid containing 2-(2-hydroxyethoxy)ethylacrylate, isobonyl acrylate, and a polymerization initiator onto anintermediate transcript, subsequently discharging an ink containing2-(2-hydroxyethoxy)ethyl acrylate, isobonyl acrylate, a polymerizationinitiator, a pigment, a dispersant, and a surfactant onto theintermediate transcript, and then transferring the ink onto a recordingmedium.

Unfortunately, the ink jet ink described in JP-T-2004-526820, thephotocurable composition described in JP-A-2008-19292, the active energyray-curable composition described in JP-A-2004-224841, and the ink usedin the image-forming method described in JP-A-2008-179136 cause problemsof being inferior curing or occurrence of wrinkles on a coating filmsurface after curing (hereinafter, also referred to as “curingwrinkles”).

Furthermore, for example, Japanese Patent Nos. 3461501 and 3544658disclose an active energy ray-curable ink jet printing ink or a reactivediluent composition composed of 2-(vinyloxyethoxy)ethyl acrylate or2-(vinyloxyethoxy)ethyl methacrylate, 2-(hydroxyethoxy)ethyl vinyl etheras a polymerizable compound containing a hydroxyl group, a colorant, anda photopolymerization initiator.

For example, JP-A-2009-62541 discloses an ink jet ink containing atleast one multifunctional (meth)acrylate monomer, at least one vinylether monomer, at least one radical photopolymerization initiator, andat least one dispersible pigment. The amount of the multifunctional(meth)acrylate monomer is 2 to 15 parts by weight based on 1 part byweight of the vinyl ether monomer, the content of the vinyl ethermonomer is 1 to 15% by weight, and the content of the multifunctional(meth)acrylate monomer is 50 to 95% by weight.

For example, JP-T-2008-507598 discloses a radiation curable ink jet inkcontaining 25.8% by weight of hexanediol diacrylate, 4.6% by weight ofan amine adduct of tripropylene glycol diacrylate, 2.3% by weight of2-(2-ethoxyethoxy)ethyl acrylate, 2.5% by weight of alkoxylatedphenoxyethyl acrylate, 3.7% by weight of2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone, 3.2% by weight of2-hydroxy-2-methylpropiophenone, 2.8% by weight of a mixture oftrimethylbenzophenone and methylbenzophenone, 0.5% by weight ofisopropylthioxanthone, 27.8% by weight of a cyan pigment dispersant, and17.6% by weight of 2-(2-vinyloxyethoxy)ethyl acrylate.

For example, JP-A-2010-157706 discloses a curable composition forphoto-imprint composed of 9.5% by mass of a monofunctional acrylicmonomer (benzyl acrylate), 9.8% by mass of 2-(2-vinyloxyethoxy)ethylacrylate, 47.3% by mass of a difunctional acrylic monomer (neopentylglycol diacrylate), 19.4% by mass of a trifunctional acrylic monomer(trimethylol propane triacrylate), 1.0% by mass of a photopolymerizationinitiator, 2.0% by mass of an antioxidant, 10.0% by mass of a couplingagent, and 1.0% by mass of a surfactant.

Unfortunately, the inks described in Japanese Patent Nos. 3461501 and3544658, JP-A-2009-62541, JP-T-2008-507598, and JP-A-2010-157706 haveproblems of being inferior in at least any of curing properties,adhesion, and photopolymerization initiator solubility.

SUMMARY

An advantage of some aspects of the invention is to provide aphotocurable ink composition that is excellent in curing property andcan prevent occurrence of curing wrinkles.

Another advantage of some aspects of the invention is to provide aphotocurable ink jet recording ink composition that is excellent incuring property, adhesion, and photopolymerization initiator solubility.

The inventors have found that the above-mentioned problems can be solvedby a photocurable ink composition containing prescribed vinyl ethergroup-containing (meth)acrylic esters, dipropylene glycoldi(meth)acrylate, monofunctional (meth)acrylate having an aromatic ringskeleton, and a coloring material.

That is, a first invention includes the following aspects.

[1] A photocurable ink composition including polymerizable compounds anda photopolymerization initiator, wherein

the polymerizable compounds include:

vinyl ether group-containing (meth)acrylic esters represented by thefollowing Formula (I):CH₂═CR¹—COOR²—O—CH═CH—R³  (I)(wherein, R¹ represents a hydrogen atom or a methyl group; R² representsa divalent organic residue having 2 to 20 carbon atoms; and R³represents a hydrogen atom or a monovalent organic residue having 1 to11 carbon atoms);

dipropylene glycol di(meth)acrylate; and

monofunctional (meth)acrylate having an aromatic ring skeleton, and

the ink composition includes a coloring material.

[2] The photocurable ink composition according to aspect [1], whereinthe content of the dipropylene glycol di(meth)acrylate is 5 to 65% bymass based on the total mass of the ink composition.

[3] The photocurable ink composition according to aspect [1] or [2],wherein the content of the monofunctional (meth)acrylate having anaromatic ring skeleton is 10 to 60% by mass based on the total mass ofthe ink composition.

[4] The photocurable ink composition according to any one of aspects [1]to [3], wherein the content of the vinyl ether group-containing(meth)acrylic esters is 10 to 65% by mass based on the total mass of theink composition.

[5] The photocurable ink composition according to any one of aspects [1]to [4], wherein the photopolymerization initiator is an acylphosphineoxide compound and is contained in an amount of 9 to 15% by mass basedon the total mass of the ink composition.

[6] The photocurable ink composition according to any one of aspects [1]to [5], wherein the ink composition is allowed to adhere to a recordingmedium and is cured by irradiation with light from an ultravioletlight-emitting diode having an emission peak wavelength in a range of350 to 420 nm.[7] The photocurable ink composition according to any one of aspects [1]to [6], wherein the ink composition is curable by irradiation with anenergy of 300 mJ/cm² or less from an ultraviolet light-emitting diodehaving an emission peak wavelength in a range of 350 to 420 nm.[8] The photocurable ink composition according to any one of aspects [1]to [7], wherein the vinyl ether group-containing (meth)acrylic estersare 2-(vinyloxyethoxy)ethyl acrylate.[9] An ink jet recording method including allowing the photocurable inkcomposition according to any one of aspects [1] to [8] to adhere to arecording medium and curing the adhering ink composition by irradiationwith light from an ultraviolet light-emitting diode having an emissionpeak wavelength in a range of 350 to 420 nm.[10] An ink jet recording apparatus for allowing the photocurable inkcomposition according to any one of aspects [1] to [8] to adhere to arecording medium and curing the adhering ink composition by irradiationwith light from an ultraviolet light-emitting diode having an emissionpeak wavelength in a range of 350 to 420 nm.

The inventors have investigated problems of the inks and thecompositions disclosed in the above-mentioned patent documents and alsoinvestigated causes of the problems. The active energy ray-curable inkjet printing ink and the reactive diluent composition disclosed inJapanese Patent Nos. 3461501 and 3544658 are particularly inferior incuring property and photopolymerization initiator solubility and have aproblem of being slightly inferior in storage stability. The inventorshave found that the problems are caused by that the hydroxylgroup-containing polymerizable compound contained in the inkdeteriorates the storage stability and also hardly contributes tophotopolymerization initiator solubility. The ink jet ink disclosed inJP-A-2009-62541 is particularly inferior in curing property and adhesionand has a problem that the viscosity increases and a recorded matterbecomes slightly inferior in flexibility. The inventors have found thatthe problems are caused by that the vinyl ether monomer having only avinyl ether group as a substituent contained in the ink hardlycontributes to the curing properties and that the multifunctional(meth)acrylate monomer is contained too much and thereby deterioratesadhesion and flexibility of a recorded matter and increases theviscosity. The radiation curable ink jet ink disclosed inJP-T-2008-507598 is inferior in curing property, adhesion, andphotopolymerization initiator solubility and has problems that theviscosity increases and the abrasion resistance slightly decreases. Theinventors have found that the problems are caused by that the amounts ofthe alkoxylated phenoxyethyl acrylate and the 2-(2-vinyloxyethoxy)ethylacrylate are low. The curable composition for photo-imprint disclosed inJP-A-2010-157706 has a problems of being inferior in curing property andadhesion. The inventors have found that the problems are mainly causedby that the content of the 2-(2-vinyloxyethoxy)ethyl acrylate is low andthereby the composition of the curable composition for photo-imprint isnot suitable as an ink jet ink.

The inventors have found that the above-mentioned problems can be solvedby a photocurable ink jet recording ink composition containing vinylether group-containing (meth)acrylic esters having a prescribedstructure and monofunctional (meth)acrylate having an aromatic ringskeleton in predetermined amounts. Thus, the invention has beenaccomplished.

That is, a second invention includes the following aspects.

[1] A photocurable ink jet recording ink composition includingpolymerizable compounds and a photopolymerization initiator, wherein

the polymerizable compounds include:

vinyl ether group-containing (meth)acrylic esters represented by thefollowing Formula (I):CH₂═CR¹—COOR²—O—CH═CH—R³  (I)(wherein, R¹ represents a hydrogen atom or a methyl group; R² representsa divalent organic residue having 2 to 20 carbon atoms; and R³represents a hydrogen atom or a monovalent organic residue having 1 to11 carbon atoms) in an amount of 45 to 80% by mass based on the totalmass of the ink composition; and

monofunctional (meth)acrylate having an aromatic ring skeleton in anamount of 5 to 40% by mass based on the total mass of the inkcomposition.

[2] The photocurable ink jet recording ink composition according toaspect [1], wherein the vinyl ether group-containing (meth)acrylicesters are 2-(vinyloxyethoxy)ethyl acrylate.

[3] The photocurable ink jet recording ink composition according toaspect [1] or [2], wherein the photopolymerization initiator is anacylphosphine oxide compound and is contained in an amount of 7% by massor more based on the total mass of the ink composition.[4] The photocurable ink jet recording ink composition according to anyone of aspects [1] to [3], wherein the content of thephotopolymerization initiator is 9% by mass or more based on the totalmass of the ink composition.[5] The photocurable ink jet recording ink composition according to anyone of aspects [1] to [4], wherein the monofunctional (meth)acrylatehaving an aromatic ring skeleton is a compound represented by thefollowing Formula (II) and/or a compound represented by the followingFormula (III):CH₂═CR⁴—COOR⁵—Ar  (II)CH₂═CR⁴—COO—Ar  (III)(R⁴ in Formulae (II) and (III) represents a hydrogen atom or a methylgroup; Ar in Formula (II) represents an aromatic ring skeleton having atleast one aryl group where a carbon atom constituting the aryl group isa monovalent organic residue binding to the group represented by R⁵; R⁵represents a divalent organic residue having 1 to 4 carbon atoms; and Arin Formula (III) represents an aromatic ring skeleton having at leastone aryl group where a carbon atom constituting the aryl group is amonovalent organic residue binding to —COO— in the formula).[6] The photocurable ink jet recording ink composition according to anyone of aspects [1] to [5], wherein the polymerizable compounds furtherinclude a tri- or more-functional (meth)acrylic monomer in an amount of3 to 22% by mass based on the total mass of the ink composition.[7] The photocurable ink jet recording ink composition according to anyone of aspects [1] to [6], wherein the polymerizable compounds furtherinclude amino (meth)acrylate in an amount of 2 to 22% by mass based onthe total mass of the ink composition.[8] The photocurable ink jet recording ink composition according to anyone of aspects [1] to [7], the ink composition having a viscosity at 25°C. of 5 to 15 mPa·s.[9] An ink jet recording method comprising a discharging step ofdischarging the photocurable ink jet recording ink composition accordingto any one of aspects [1] to [8] onto a recording medium; and a curingstep of curing the photocurable ink jet recording ink compositiondischarged in the discharging step by irradiating the photocurable inkjet recording ink composition with ultraviolet light.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiment according to the first invention will now be described indetail. The invention is not limited to the following embodiments, andvarious modifications can be made within the scope of the invention.

Throughout the first invention, the term “(meth)acrylate” refers toacrylate and/or methacrylate corresponding to the acrylate, and“(meth)acrylic” refers to acrylic and/or methacrylic corresponding tothe acrylic.

Throughout the first invention, the term “curing property” refers to aproperty of curing upon exposure to light. The term “adhesion” refers toa property that a coating film is hardly detached from a substratesurface. The term “abrasion resistance” refers to a property that acured material is hardly detached from a recording material when thecured material is rubbed. The term of “storage stability” refers to aproperty that the viscosity of an ink hardly varies between before andafter storage of the ink at 60° C. for one week.

Photocurable Ink Composition

The photocurable ink composition (hereinafter, also simply referred toas “ink composition”) according to an embodiment of the inventionincludes polymerizable compounds and a photopolymerization initiator.The polymerizable compounds include vinyl ether group-containing(meth)acrylic esters represented by the following Formula (I):CH₂═CR¹—COOR²—O—CH═CH—R³  (I)(wherein, R¹ represents a hydrogen atom or a methyl group; R² representsa divalent organic residue having 2 to 20 carbon atoms; and R³represents a hydrogen atom or a monovalent organic residue having 1 to11 carbon atoms), dipropylene glycol di(meth)acrylate, andmonofunctional (meth)acrylate having an aromatic ring skeleton, and theink composition includes a coloring material. Additives (components)that are contained or optionally contained in the ink composition of theembodiment will now be described.Polymerizable Compounds

The polymerizable compounds contained in the ink composition of theembodiment polymerize by the effect of the photopolymerization initiatordescribed below when irradiated with ultraviolet light to harden theprinted ink. Vinyl ether group-containing (meth)acrylic esters

The vinyl ether group-containing (meth)acrylic esters, which arepolymerizable compounds indispensable in the embodiment, are representedby Formula (I).

An ink composition containing a predetermined amount of the vinyl ethergroup-containing (meth)acrylic esters can make the curing properties ofan ink satisfactory and also can decrease the viscosity of the ink.

In Formula (I), the divalent organic residue having 2 to 20 carbon atomsrepresented by R² is preferably an optionally substituted linear,branched, or circular alkylene group having 2 to 20 carbon atoms, anoptionally substituted alkylene group having 2 to 20 carbon atoms and anoxygen atom involved in an ether bond and/or an ester bond in itsstructure, or an optionally substituted divalent aromatic group having 6to 11 carbon atoms. Among them, more preferred are alkylene groupshaving 2 to 6 carbon atoms, such as an ethylene group, an n-propylenegroup, an isopropylene group, and a butylene group; and alkylene grouphaving 2 to 9 carbon atoms and an oxygen atom involved in an ether bondin its structure, such as an oxyethylene group, an oxy-n-propylenegroup, an oxyisopropylene group, and an oxybutylene group.

In Formula (I), the monovalent organic residue having 1 to 11 carbonatoms represented by R³ is preferably an optionally substituted linear,branched, or circular alkyl group having 1 to 10 carbon atoms or anoptionally substituted aromatic group having 6 to 11 carbon atoms. Amongthem, more preferred are alkyl groups having one or two carbon atoms,such as a methyl group and an ethyl group, and aromatic groups having 6to 8 carbon atoms, such as a phenyl group and a benzyl group.

When the organic residues have substituents, the substituents areclassified into groups containing carbon atoms and groups not containingcarbon atoms. In the case of a substituent containing a carbon atom, thecarbon atom is counted as the carbon atom of the organic residue.Examples of the group containing a carbon atom include, but not limitedto, carboxyl groups and alkoxy groups. Examples of the group notcontaining a carbon atom include, but not limited to, hydroxyl groupsand halo groups.

Examples of the vinyl ether group-containing (meth)acrylic estersinclude, but not limited to, 2-vinyloxyethyl (meth)acrylate,3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl(meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl(meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate,1-vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl(meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate,3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl(meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl(meth)acrylate, 6-vinyloxyhexyl (meth)acrylate,4-vinyloxymethylcyclohexylmethyl (meth)acrylate,3-vinyloxymethylcyclohexylmethyl (meth)acrylate,2-vinyloxymethylcyclohexylmethyl (meth)acrylate,p-vinyloxymethylphenylmethyl (meth)acrylate,m-vinyloxymethylphenylmethyl (meth)acrylate,o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl(meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl(meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxy)propyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate, 2(vinyloxyisopropoxyethoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,polyethylene glycol monovinyl ether (meth)acrylate, and polypropyleneglycol monovinyl ether (meth)acrylate.

Among them, 2-(vinyloxyethoxy)ethyl (meth)acrylate, i.e.,2-(vinyloxyethoxy)ethyl acrylate and 2-(vinyloxyethoxy)ethylmethacrylate can notably decrease the viscosity of an ink, have a highflash point, and can provide excellent curing properties to an ink andare therefore preferred. 2-(Vinyloxyethoxy)ethyl acrylate is morepreferred. 2-(Vinyloxyethoxy)ethyl (meth)acrylate includes2-(2-vinyloxyethoxy)ethyl (meth)acrylate and 2-(1-vinyloxyethoxy)ethyl(meth)acrylate. 2-(Vinyloxyethoxy)ethyl acrylate includes2-(2-vinyloxyethoxy)ethyl acrylate and 2-(1-vinyloxyethoxy)ethylacrylate. 2-(Vinyloxyethoxy)ethyl acrylate is superior to2-(vinyloxyethoxy)ethyl methacrylate in the light of curing property.

The content of the vinyl ether group-containing (meth)acrylic esters ispreferably 5 to 65% by mass, more preferably 10 to 65% by mass, and mostpreferably 20 to 65% by mass, based on the total mass (100% by mass) ofthe ink composition. Within the content range above, the ink can haveexcellent curing properties, and curing wrinkles can be prevented fromoccurring. In order to further effectively prevent occurrence of curingwrinkles and to obtain excellent storage stability, the content ispreferably 35% by mass or less, more preferably 30% by mass or less,based on the total mass (100% by mass) of the ink composition.

The vinyl ether group-containing (meth)acrylic esters can be producedby, for example, but not limited to, a method (process B) of esterifying(meth)acrylic acid and hydroxyl group-containing vinyl ether; a method(process C) of esterifying a (meth)acrylic acid halide and hydroxylgroup-containing vinyl ether; a method (process D) of esterifying a(meth)acrylic anhydride and hydroxyl group-containing vinyl ether; amethod (process E) of ester exchanging (meth)acrylic ester and hydroxylgroup-containing vinyl ether; a method (process F) of esterifying a(meth)acrylic acid and halogen-containing vinyl ether; a method (processG) of esterifying an alkaline (earth) metal salt of (meth)acrylic acidand halogen-containing vinyl ether; a method (process H) of vinylexchanging hydroxyl group-containing (meth)acrylic ester and vinylcarboxylate; or a method (process I) of ether exchanging hydroxylgroup-containing (meth)acrylic ester and alkyl vinyl ether.

Among these methods, process E can exhibit higher effects desired in theembodiment and is therefore preferred. Polymerizable compound other thanvinyl ether group-containing (meth)acrylic esters

The ink composition according to the embodiment also containsdipropylene glycol di(meth)acrylate, in addition to the vinyl ethergroup-containing (meth)acrylic esters. An ink composition containing apredetermined amount of the dipropylene glycol di(meth)acrylate canprovide satisfactory curing properties and abrasion resistance and alsocan prevent occurrence of curing wrinkles. As the dipropylene glycoldi(meth)acrylate, dipropylene glycol diacrylate can particularly exhibithigher effects and is more preferred.

The content of the dipropylene glycol di(meth)acrylate is preferably 3to 70% by mass, more preferably 5 to 65% by mass, and most preferably 10to 30% by mass, based on the total mass (100% by mass) of the inkcomposition. Within the content range above, the ink can have excellentcuring properties and abrasion resistance, and occurrence of curingwrinkles can be prevented. In order to further improve the adhesion, thecontent is preferably 30 to 65% by mass and more preferably 30 to 50% bymass.

In addition to the vinyl ether group-containing (meth)acrylic esters andthe dipropylene glycol di(meth)acrylate, the ink composition may furthercontain various known monomers and oligomers, such as monofunctional,difunctional, and tri- or more-functional monomers and oligomers(hereinafter, referred to as “other polymerizable compound”). Examplesof the monomer include unsaturated carboxylic acids (e.g., (meth)acrylicacid, itaconic acid, crotonic acid, isocrotonic acid, and maleic acid,and salts and esters thereof), urethanes, amides and anhydrides thereof,acrylonitrile, styrene, various unsaturated polyesters, unsaturatedpolyethers, unsaturated polyamides, and unsaturated urethanes. Examplesof the oligomer include oligomers formed from the monomers mentionedabove (e.g., linear acrylic oligomers), epoxy (meth)acrylate, oxetane(meth)acrylate, aliphatic urethane (meth)acrylate, aromatic urethane(meth)acrylate, and polyester (meth)acrylate.

As the other monofunctional monomer or multifunctional monomer, anN-vinyl compound may be used. Examples of the N-vinyl compound includeN-vinyl formamide, N-vinyl carbazole, N-vinyl acetamide, N-vinylpyrrolidone, N-vinylcaprolactam, and acryloylmorpholine, and derivativesthereof.

Among other polymerizable compounds, ester of (meth)acrylic acid, i.e.,(meth)acrylate is preferable.

In the (meth)acrylates mentioned above, examples of the monofunctional(meth)acrylate include isoamyl (meth)acrylate, stearyl (meth)acrylate,lauryl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate,isomyristyl (meth)acrylate, isostearyl (meth)acrylate,2-ethylhexyl-diglycol (meth)acrylate, 2-hydroxybutyl (meth)acrylate,butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate,methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol(meth)acrylate, methoxypropylene glycol (meth)acrylate, phenoxyethyl(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,lactone-modified flexible (meth)acrylate, t-butylcyclohexyl(meth)acrylate, dicyclopentanyl (meth)acrylate, anddicyclopentenyloxyethyl (meth)acrylate. Among these monofunctional(meth)acrylates, phenoxyethyl (meth)acrylate, in particular,phenoxyethyl acrylate, exhibits good compatibility with thephotopolymerization initiator and is therefore preferred.

In the (meth)acrylates mentioned above, examples of the difunctional(meth)acrylate excluding the dipropylene glycol di(meth)acrylate includetriethylene di(meth)acrylate, tetraethylene glycol di(meth)acrylate,polyethylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate,dimethylol-tricyclodecane di(meth)acrylate, EO (ethylene oxide) adductdi(meth)acrylate of bisphenol A, PO (propylene oxide) adductdi(meth)acrylate of bisphenol A, hydroxypivalic acid neopentyl glycoldi(meth)acrylate, and polytetramethylene glycol di(meth)acrylate.

In the (meth)acrylates mentioned above, examples of the tri- ormore-functional (meth)acrylate include trimethylolpropanetri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate,pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol hexa(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, glycerin propoxy tri(meth)acrylate,caprolactone-modified trimethylolpropane tri(meth)acrylate,pentaerythritolethoxy tetra(meth)acrylate, and caprolactam-modifieddipentaerythritol hexa(meth)acrylate.

Among these compounds, the other polymerizable compound preferablyincludes monofunctional (meth)acrylate. In such a case, the inkcomposition can have a low viscosity and high storage stability, andexcellent discharge stability can be easily obtained in recording by anink jet system. Furthermore, a combination use of monofunctional(meth)acrylate, preferably phenoxyethyl (meth)acrylate, and difunctional(meth)acrylate, preferably dipropylene glycol di(meth)acrylate,increases the toughness, heat resistance, and chemical resistance of acoating film, and, therefore, such a use is preferred.

The monofunctional (meth)acrylate preferably has one or more skeletonsselected from the group consisting of saturated alicyclic skeletons andunsaturated alicyclic skeletons. Examples of the monofunctional(meth)acrylate having a saturated alicyclic skeleton include isobornyl(meth)acrylate, t-butylcyclohexyl (meth)acrylate, and dicyclopentanyl(meth)acrylate. Examples of the monofunctional (meth)acrylate having anunsaturated alicyclic skeleton include dicyclopentenyloxyethyl(meth)acrylate. When the other polymerizable compound is themonofunctional (meth)acrylate having the skeleton mentioned above, theink composition can have a low viscosity.

The ink composition of the embodiment further contains monofunctional(meth)acrylate having an aromatic ring skeleton. Examples of themonofunctional (meth)acrylate having an aromatic ring skeleton includephenoxyethyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,benzyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate,nonylphenoxyethyl (meth)acrylate, and alkoxylated phenoxyethyl(meth)acrylate. The ink composition containing the monofunctional(meth)acrylate having an aromatic ring skeleton exhibits goodcompatibility with additives such as the photopolymerization initiator,has satisfactory curing properties, and is prevented from occurrence ofcuring wrinkles.

Among these compounds, from the viewpoints of the curing properties andthe initiator solubility, phenoxyethyl (meth)acrylate,2-hydroxy-3-phenoxypropyl (meth)acrylate, and benzyl (meth)acrylate arepreferred. Phenoxyethyl acrylate exhibits good compatibility withadditives such as the photopolymerization initiator and can decreaseviscosity and odor and is therefore preferred.

The content of the monofunctional (meth)acrylate having an aromatic ringskeleton is preferably 5 to 70% by mass, more preferably 10 to 60% bymass, more preferably 10 to 60% by mass, more preferably 10 to 45% bymass, more preferably 10 to 30% by mass, and most preferably 10 to 25%by mass, based on the total mass (100% by mass) of the ink composition.Within the content range above, the compatibility with additives such asthe photopolymerization initiator can be further increased.

In the case where the ink composition of the embodiment contains apolymerizable compound in addition to the vinyl ether group-containing(meth)acrylic esters, the dipropylene glycol di(meth)acrylate, and themonofunctional (meth)acrylate having an aromatic ring skeleton, thecontent of the polymerizable compound is preferably 40% by mass or less,more preferably 20 to 40% by mass, based on the total mass (100% bymass) of the ink composition. Within the content range above, thesolubility of the additives is excellent, and a coating film having hightoughness, heat resistance, and chemical resistance can be formed.

The polymerizable compounds may be used alone or in a combination of twoor more thereof.

Photopolymerization Initiator

The photopolymerization initiator contained in the ink composition ofthe embodiment allows an ink present on a recording medium surface tocure by photopolymerization under ultraviolet irradiation to achieveprinting. In radiation, ultraviolet (UV) is excellent in safety, and thelight source lamp thereof is inexpensive. The photopolymerizationinitiator may be any one that generates active species such as radicalsand cations by light (ultraviolet) energy and thereby initiatespolymerization of the polymerizable compound. For example, aphoto-radial polymerization initiator or a photo-cation polymerizationinitiator can be used. The photo-radial polymerization initiator isparticularly preferred.

Examples of the photo-radial polymerization initiator include aromaticketones, acylphosphine oxide compounds, aromatic onium salt compounds,organic peroxides, thio compounds (e.g., thioxanthone compounds andthiophenyl group-containing compounds), hexaarylbiimidazole compounds,ketoxime ester compounds, borate compounds, azinium compounds,metallocene compounds, active ester compounds, compounds havingcarbon-halogen bonds, and alkylamine compounds.

Among these compounds, in particular, the acylphosphine oxide compoundand the thioxanthone compound can improve the curing properties of anink, and at least one of them, in particular, the acylphosphine oxidecompound is preferred. When the ink composition of the embodimentcontains the acylphosphine oxide compound, the content thereof ispreferably 7 to 15% by mass, more preferably 9 to 15% by mass, based onthe total mass (100% by mass) of the ink composition. Within thiscontent range, the solubility of the compound in the ink composition issatisfactory, and the ink composition can have excellent curingproperties.

More preferred is to contain both the acylphosphine oxide compound andthe thioxanthone compound as the photo-radial polymerization initiator.

Specific examples of the photo-radial polymerization initiator includeacetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenylketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone,4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether,benzoin ethyl ether, benzyl dimethyl ketal,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone,diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide,2,4-diethylthioxanthone, andbis-(2,6-dimethoxybenzoyl)-2,4,4-tiemethylpentylphosphine oxide.

Examples of commercially available photo-radial polymerization initiatorinclude IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethan-1-one), IRGACURE184 (1-hydroxy-cyclohexyl-phenyl-ketone), 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one),IRGACURE 127(2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl]-2-methyl-propan-1-one}),IRGACURE 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one),IRGACURE 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), IRGACURE379(2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone),DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), IRGACURE 784(bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium),IRGACURE OXE 01 (1,2-octanedione, 1-[4-(phenylthio)-,2-(O-benzoyloxime)]), IRGACURE OXE 02 (ethanone,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime)),IRGACURE 754 (oxyphenylacetic acid, 2-[2-oxo-2-phenylacetoxyethoxy]ethylester, and a mixture of oxyphenylacetic acid and2-(2-hydroxyethoxy)ethyl ester) (each manufactured by BASF), KAYACUREDETX-S (2,4-diethylthioxanthone) (manufactured by Nippon Kayaku Co.,Ltd.), Lucirin TPO, LR8893, and LR8970 (each manufactured by BASF), andUbecryl P36 (manufactured by UCB).

The photopolymerization initiators may be used alone or in a combinationof two or more thereof.

In order to sufficiently accelerate ultraviolet curing speed and, at thesame time, to avoid insufficient dissolution of the photopolymerizationinitiator and avoid coloring due to the photopolymerization initiator,the content of the photopolymerization initiator is preferably 1 to 20%by mass, more preferably 5 to 15% by mass, based on the total mass (100%by mass) of the ink composition.

Coloring Material

The ink composition of the embodiment further contains a coloringmaterial. The coloring material can be a pigment and/or a dye.

Pigment

In the embodiment, the use of a pigment as the coloring material canincrease the light resistance of the ink composition. The pigment may bean inorganic pigment or an organic pigment.

As the inorganic pigment, for example, carbon blacks (e.g., C.I. PigmentBlack 7), such as furnace black, lamp black, acetylene black, andchannel black; iron oxide; and titanium oxide can be used.

Examples of the organic pigment include azo pigments, such as insolubleazo pigments, condensed azo pigments, azo lake, and chelate azopigments; polycyclic pigments, such as phthalocyanine pigments, peryleneand perinone pigments, anthraquinone pigments, quinacridone pigments,dioxane pigments, thioindigo pigments, isoindolinone pigments, andquinophthalone pigments; dye chelates (e.g., basic dye chelates and aciddye chelates); dye lakes (e.g., basic dye lakes and acid dye lakes); andnitro pigments, nitroso pigments, aniline black, and daylightfluorescent pigments.

More specifically, examples of the carbon black used in black inksinclude No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7,MA8, MA100, and No. 2200B (trade names of products manufactured byMitsubishi Chemical Corporation); Raven 5750, Raven 5250, Raven 5000,Raven 3500, Raven 1255, and Raven 700 (trade names of productsmanufactured by Carbon Columbia); Regal 400R, Regal 330R, Regal 660R,Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch1000, Monarch 1100, Monarch 1300, and Monarch 1400 (trade names ofproducts manufactured by CABOT JAPAN K.K.); and Color Black FW1, ColorBlack FW2, Color Black FW2V, Color Black FW18, Color Black FW200, ColorBlack S150, Color Black 5160, Color Black 5170, Printex 35, Printex U,Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black4A, and Special Black 4 (trade names of products manufactured byDegussa).

Examples of the pigment used in white inks include C.I. Pigment White 6,18, and 21.

Examples of the pigment used in yellow inks include C.I. Pigment Yellow1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55,65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114,117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172,and 180.

Examples of the pigment used in magenta inks include C.I. Pigment Red 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23,30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112,114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177,178, 179, 184, 185, 187, 202, 209, 219, 224, and 245; and C.I. PigmentViolet 19, 23, 32, 33, 36, 38, 43, and 50.

Examples of the pigment used in cyan inks include C.I. Pigment Blue 1,2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, and 66;and C.I. Vat Blue 4 and 60.

Examples of the pigment other than magenta, cyan, and yellow pigmentsinclude C.I. Pigment Green 7 and 10; C.I. Pigment Brown 3, 5, 25, and26; and C.I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38,40, 43, and 63.

These pigments may be used alone or in a combination of two or morethereof.

Dye

In the embodiment, the coloring material may be a dye. Any dye, such asacid dyes, direct dyes, reactive dyes, and basic dyes, can be used.Examples of the dye include C.I. Acid Yellow 17, 23, 42, 44, 79, and142; C.I. Acid Red 52, 80, 82, 249, 254, and 289; C.I. Acid Blue 9, 45,and 249; C.I. Acid Black 1, 2, 24, and 94; C.I. Food Black 1 and 2; C.I.Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, and 173;C.I. Direct Red 1, 4, 9, 80, 81, 225, and 227; C.I. Direct Blue 1, 2,15, 71, 86, 87, 98, 165, 199, and 202; C.I. Direct Black 19, 38, 51, 71,154, 168, 171, and 195; C.I. Reactive Red 14, 32, 55, 79, and 249; andC.I. Reactive Black 3, 4, and 35.

These dyes may be used alone or in a combination of two or more thereof.

The content of the coloring material is preferably 1 to 20% by massbased on the total mass (100% by mass) of the ink composition. Withinthe content range, satisfactory color-developing properties can beobtained, and prevention of curing of a coating film due to lightabsorption by the coloring material itself can be decreased.

The ink composition of the embodiment can color a recording medium bycontaining the coloring material mentioned above and thereby can performrecording on the recording medium. Though the ink composition of theembodiment contains a coloring material, the ink composition can haveexcellent curing properties, adhesion, and abrasion resistance, andoccurrence of curing wrinkles can be prevented.

Dispersant

When the ink composition of the embodiment contains a pigment, the inkcomposition may further contain a dispersant for well dispersing thepigment. Any dispersant can be used. For example, a dispersant that iscommonly used for preparing a pigment-dispersed liquid, such as apolymer dispersant, can be used. Specific examples of such a dispersantinclude those of which main component is at least one selected frompolyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers,acrylic polymers and copolymers, polyesters, polyamides, polyimides,polyurethanes, amino polymers, silicon-containing polymers,sulfur-containing polymers, fluorine-containing polymers, and epoxyresins. Examples of commercially available polymer dispersants includeAjisper series (trade name) manufactured by Ajinomoto Fine-Techno,Solsperse series (e.g., Solsperse 36000 (trade name) available fromAvecia Co.), Disperbyk series (trade name) manufactured by BYK Chemie,and Disparlon series (trade name) manufactured by Kusumoto Chemicals.

Other Additives

The ink composition of the embodiment may contain additives (components)in addition to the above-described additives. Such components are notparticularly limited. For example, generally known surfactant,polymerization inhibitor, penetration accelerator, and wetting agent(moisturizing agent), and other additives can be used. Examples of theother additive include generally known fixing agent, antifungal agent,preservative, antioxidant, UV absorber, chelating agent, pH adjuster,and thickener.

Recording Medium

The ink composition of the embodiment is discharged on a recordingmedium by a recording method described below to form a recorded matter.The recording medium may be absorbable or nonabsorbable. The recordingmethod of the embodiment described below can be widely applied tovarious recording media exhibiting highly different degrees ofabsorbability, i.e., from non-absorbing media into which aqueous inkhardly permeates to absorbing media into which aqueous ink easilypermeates. In the case of applying the ink composition to anon-absorbing recording medium, for example, a drying step may berequired after curing the ink composition by exposure to ultravioletlight.

Any absorbing recording medium can be used, and examples thereof includeplain paper such as electrophotographic paper highly absorbing aqueousinks, ink jet paper (special paper for ink jet printing and having anink absorbing layer containing silica particles or alumina particles oran ink absorbing layer made of a hydrophilic polymer such as polyvinylalcohol (PVA) or polyvinyl pyrrolidone (PVP)), and paper showingrelatively low absorbability for aqueous inks and used in ordinaryoffset printing, such as art paper, coated paper, and cast-coated paper.

Any non-absorbing recording medium can be used, and examples thereofinclude films and plates of plastics such as polyvinyl chloride (PVC),polyethylene, polypropylene, and polyethylene terephthalate (PET);plates of metals such as iron, silver, copper, and aluminum; metalplates coated with such various metals by vapor deposition; plasticfilms; and plates of alloys such as stainless steel and brass.

Recording Method

An embodiment of the invention relates to a recording method. Thephotocurable ink composition according to the embodiment described abovecan be used in the recording method of this embodiment. The recordingmethod can be applied to an ink jet system. The recording methodincludes a discharging step of discharging the above-described inkcomposition onto a recording medium; and a curing step of curing the inkcomposition discharged in the discharging step by irradiating the inkcomposition with ultraviolet light. The ink composition thus cured onthe recording medium forms a coating film (cured film).

As the method of allowing the ink composition to adhere to a recordingmedium, various plate printing systems can be employed as well as theink jet system. The ink jet system can use a small-sized recordingapparatus, can be applied to on-demand printing, and can record highlyfine images with high resolution and is therefore preferred.

Discharging Step

In the discharging step, an ink composition is discharged onto arecording medium so that the ink composition adheres to the recordingmedium. The ink composition at the time of being discharged preferablyhas a viscosity of 5 to 30 mPa·s. In the case of an ink compositionhaving such a viscosity at room temperature or in a non-heated state,the ink composition may be discharged at room temperature or withoutheating. Alternatively, an ink composition may be heated to apredetermined temperature to adjust the viscosity to a proper level andmay be then discharged. Thus, satisfactory discharge stability isachieved.

The photocurable ink composition of the embodiment has a higherviscosity than those of ordinary aqueous ink compositions. The viscositytherefore largely varies depending on changes in temperature when theink composition is discharged. The change in viscosity of the ink highlyaffects the sizes of droplets and the droplet-discharging speed, whichmay cause deterioration in image quality. Accordingly, it is preferredto maintain the temperature of the ink at the time of being dischargedas constant as possible.

Curing Step

Subsequently, the ink composition discharged and adhering to therecording medium is cured by light (ultraviolet) irradiation in thecuring step. This is caused by that the photopolymerization initiatorcontained in the ink composition is decomposed by ultravioletirradiation to generate initiation species such as radicals, acids, orbases and that polymerization of the polymerizable compound isaccelerated by the function of the initiation species, or is caused bythat polymerization of the polymerizable compound starts by ultravioletirradiation. If the ink composition contains a sensitizing dye togetherwith the photopolymerization initiator, the sensitizing dye in thesystem absorbs ultraviolet light and thereby changes to an excitedstate, which accelerates decomposition of the photopolymerizationinitiator by contact therewith. As a result, more sensitive curingreaction is achieved.

As the ultraviolet light source, a mercury lamp or a gas/solid laser ismainly used. As light sources for curing photocurable ink compositions,mercury lamps and metal halide lamps are widely used. However, from theviewpoint of environmental protection, it is highly desired to bemercury-free, and replacement by GaN-based semiconductor ultravioletlight emitting devices is very useful industrially and environmentally.In addition, ultraviolet light-emitting diodes (UV-LEDs) and ultravioletlight-emitting laser diodes (UV-LDs) are small-sized and have long lifeand high efficiency and are low in cost, power consumption, and heatgeneration, and are therefore expected as light sources for photocurableink jet recording. Among them, UV-LEDs are preferred. Hereinafter,UV-LED and UV-LD are collectively referred to as an ultravioletlight-emitting diode. The use of the ultraviolet light-emitting diodehas advantages mentioned above as a light source, but tends to decreasethe curing properties of an ink composition and to cause curingwrinkles.

When a UV-LED preferably having an emission peak wavelength in a rangeof 350 to 420 nm is used, a preferred photocurable ink composition iscurable by irradiation with an energy of, preferably, 300 mJ/cm² orless, more preferably 200 mJ/cm² or less, and most preferably 150 mJ/cm²or less. In such a case, a high printing speed can be obtained at lowcost. Such an ink composition can be obtained by containing aphotopolymerization initiator that is decomposed by exposure toultraviolet light having a wavelength in the above-mentioned rangeand/or a polymerizable compound that starts polymerization by exposureto ultraviolet light having a wavelength in the above-mentioned range.

Recording Apparatus

An embodiment of the invention relates to a recording apparatus. Therecording apparatus performs recording by the above-described recordingmethod on a recording medium and preferably includes a device forallowing an ink composition to adhere to a recording medium and a lightsource for irradiating the adhering ink composition with light to causecuring of the ink. The photocurable ink composition of theabove-described embodiment can be used in the recording apparatus ofthis embodiment. The recording apparatus can be preferably applied to anink jet system.

Thus, according to the embodiment, it is possible to provide aphotocurable ink composition that has excellent curing properties, canprevent occurrence of curing wrinkles, and also has high adhesion,abrasion resistance, and storage stability and to provide a recordingmethod and a recording apparatus using the ink composition.

Embodiments according to the second invention will now be described indetail. The invention is not limited to the following embodiments, andvarious modifications can be made within the scope of the invention.

Throughout the second invention, the term “(meth)acrylate” refers toacrylate and/or methacrylate corresponding to the acrylate, and“(meth)acrylic” refers to acrylic and/or methacrylic corresponding tothe acrylic.

Throughout the second invention, the term “curing” refers to that an inkcontaining a polymerizable compound solidifies by polymerization of thepolymerizable compound by exposure to radiation. The term “curingproperty” refers to a property of curing upon exposure to light. Theterm “adhesion” refers to a property that a coating film of an ink ishardly detached from a substrate surface and particularly, in Examplesbelow, refers to such a property when a rectangular lattice pattern iscut into a cured material so as to reach the surface of the recordingmedium. The term “abrasion resistance” refers to a property that a curedmaterial is hardly detached from a recording material when the curedmaterial is scratched. The term of “storage stability” refers to aproperty that the viscosity of an ink hardly varies between before andafter storage of the ink at 60° C. for one week.

Throughout the second invention, the term “recorded matter” refers to acured material formed by an ink recorded on a recording medium. Thecured material in the second invention means a hardened materialincluding a cured film and a coating film of an ink.

Photocurable Ink Jet Recording Ink Composition

The photocurable ink jet recording ink composition (hereinafter, alsosimply referred to as “ink composition”) according to an embodiment ofthe invention includes polymerizable compounds and a photopolymerizationinitiator. The polymerizable compounds include vinyl ethergroup-containing (meth)acrylic esters represented by the followingFormula (I):CH₂═CR¹—COOR²—O—CH═CH—R³  (I)(wherein, R² represents a hydrogen atom or a methyl group; R² representsa divalent organic residue having 2 to 20 carbon atoms; and R³represents a hydrogen atom or a monovalent organic residue having 1 to11 carbon atoms) and monofunctional (meth)acrylate having an aromaticring skeleton, at predetermined amounts.

Additives (components) that are contained or optionally contained in theink composition of the embodiment will now be described.

Polymerizable Compounds

The polymerizable compounds contained in the ink composition of theembodiment polymerize by the effect of the photopolymerization initiatordescribed below when irradiated with ultraviolet light to harden theprinted ink.

Vinyl Ether Group-Containing (Meth)Acrylic Esters

The vinyl ether group-containing (meth)acrylic esters, which arepolymerizable compounds indispensable in the embodiment, are representedby Formula (I).

An ink composition containing a predetermined amount of the vinyl ethergroup-containing (meth)acrylic esters can make the curing properties ofan ink satisfactory and also can decrease the viscosity of the ink.Furthermore, the curing properties of an ink when a compound having botha vinyl ether group and a (meth)acrylic group in a single molecule isused is higher than those when a compound having a vinyl ether group anda compound having a (meth)acrylic group are used.

In Formula (I), the divalent organic residue having 2 to 20 carbon atomsrepresented by R² is preferably an optionally substituted linear,branched, or circular alkylene group having 2 to 20 carbon atoms, anoptionally substituted alkylene group having 2 to 20 carbon atoms and anoxygen atom involved in an ether bond and/or an ester bond in itsstructure, or an optionally substituted divalent aromatic group having 6to 11 carbon atoms. Among them, more preferred are alkylene groupshaving 2 to 6 carbon atoms, such as an ethylene group, an n-propylenegroup, an isopropylene group, and a butylene group; and alkylene grouphaving 2 to 9 carbon atoms and an oxygen atom involved in an ether bondin its structure, such as an oxyethylene group, an oxy-n-propylenegroup, an oxyisopropylene group, and an oxybutylene group.

In Formula (I), the monovalent organic residue having 1 to 11 carbonatoms represented by R³ is preferably an optionally substituted linear,branched, or circular alkyl group having 1 to 10 carbon atoms or anoptionally substituted aromatic group having 6 to 11 carbon atoms. Amongthem, more preferred are alkyl groups having 1 or 2 carbon atoms, suchas a methyl group and an ethyl group, and aromatic groups having 6 to 8carbon atoms, such as a phenyl group and a benzyl group.

When the organic residues have substituents, the substituents areclassified into groups containing carbon atoms and groups not containingcarbon atoms. In the case of a substituent containing a carbon atom, thecarbon atom is counted as the carbon atom of the organic residue.Examples of the group containing a carbon atom include, but not limitedto, carboxyl groups and alkoxy groups. Examples of the group notcontaining a carbon atom include, but not limited to, hydroxyl groupsand halo groups.

Examples of the vinyl ether group-containing (meth)acrylic estersinclude, but not limited to, 2-vinyloxyethyl (meth)acrylate,3-vinyloxypropyl (meth)acrylate, 1-methyl-2-vinyloxyethyl(meth)acrylate, 2-vinyloxypropyl (meth)acrylate, 4-vinyloxybutyl(meth)acrylate, 1-methyl-3-vinyloxypropyl (meth)acrylate, 1vinyloxymethylpropyl (meth)acrylate, 2-methyl-3-vinyloxypropyl(meth)acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth)acrylate,3-vinyloxybutyl (meth)acrylate, 1-methyl-2-vinyloxypropyl(meth)acrylate, 2-vinyloxybutyl (meth)acrylate, 4-vinyloxycyclohexyl(meth)acrylate, 6-vinyloxyhexyl (meth)acrylate,4-vinyloxymethylcyclohexylmethyl (meth)acrylate,3-vinyloxymethylcyclohexylmethyl (meth)acrylate,2-vinyloxymethylcyclohexylmethyl (meth)acrylate,p-vinyloxymethylphenylmethyl (meth)acrylate,m-vinyloxymethylphenylmethyl (meth)acrylate,o-vinyloxymethylphenylmethyl (meth)acrylate, 2-(vinyloxyethoxy)ethyl(meth)acrylate, 2-(vinyloxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxy)propyl (meth)acrylate, 2-(vinyloxyethoxy)isopropyl(meth)acrylate, 2-(vinyloxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxy)propyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)propyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)propyl (meth)acrylate,2-(vinyloxyethoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyethoxy)isopropyl (meth)acrylate,2-(vinyloxyisopropoxyisopropoxy)isopropyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(vinyloxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxy)ethyl (meth)acrylate,2-(isopropenoxyethoxyethoxyethoxyethoxy)ethyl (meth)acrylate,polyethylene glycol monovinyl ether (meth)acrylate, and polypropyleneglycol monovinyl ether (meth)acrylate.

Among them, 2-(vinyloxyethoxy)ethyl (meth)acrylate, i.e.,2-(vinyloxyethoxy)ethyl acrylate and/or 2-(vinyloxyethoxy)ethylmethacrylate, can notably decrease the viscosity of an ink, has a highflash point, and can provide excellent curing properties to an ink, andis therefore preferred. 2-(Vinyloxyethoxy)ethyl acrylate is morepreferred. In particular, both 2-(vinyloxyethoxy)ethyl acrylate and2-(vinyloxyethoxy)ethyl methacrylate have simple structures, have lowmolecular weights, and thereby can notably decrease the viscosity of anink. 2-(Vinyloxyethoxy)ethyl (meth)acrylate includes2-(2-vinyloxyethoxy)ethyl (meth)acrylate and 2-(1-vinyloxyethoxy)ethyl(meth)acrylate. 2-(Vinyloxyethoxy)ethyl acrylate includes2-(2-vinyloxyethoxy)ethyl acrylate and 2-(1-vinyloxyethoxy)ethylacrylate. 2-(Vinyloxyethoxy)ethyl acrylate is superior to2-(vinyloxyethoxy)ethyl methacrylate in the light of curing property.

The content of the vinyl ether group-containing (meth)acrylic esters is45 to 80% based on the total mass (100% by mass) of the ink composition.A content of 45% by mass or more can provide excellent adhesion andsatisfactory curing properties and abrasion resistance. A content of 80%by mass or less provides high photopolymerization initiator solubilityand satisfactory abrasion resistance. In order to obtain furtherexcellent adhesion, abrasion resistance, and photopolymerizationinitiator solubility, the content is preferably 47 to 77% by mass, morepreferably 52 to 72% by mass, based on the total mass (100% by mass) ofthe ink composition.

The vinyl ether group-containing (meth)acrylic esters can be producedby, for example, but not limited to, a method (process B) of esterifying(meth)acrylic acid and hydroxyl group-containing vinyl ether; a method(process C) of esterifying a (meth)acrylic acid halide and hydroxylgroup-containing vinyl ether; a method (process D) of esterifying a(meth)acrylic anhydride and hydroxyl group-containing vinyl ether; amethod (process E) of ester exchanging (meth)acrylic ester and hydroxylgroup-containing vinyl ether; a method (process F) of esterifying a(meth)acrylic acid and halogen-containing vinyl ether; a method (processG) of esterifying an alkaline (earth) metal salt of (meth)acrylic acidand halogen-containing vinyl ether; a method (process H) of vinylexchanging hydroxyl group-containing (meth)acrylic ester and vinylcarboxylate; or a method (process I) of ether exchanging hydroxylgroup-containing (meth)acrylic ester and alkyl vinyl ether.

Among these methods, process E can exhibit higher effects desired in theembodiment and is therefore preferred. Monofunctional (meth)acrylatehaving an aromatic ring skeleton)

The ink composition of the embodiment contains monofunctional(meth)acrylate having an aromatic ring skeleton in addition to the vinylether group-containing (meth)acrylic esters. The ink compositioncontaining the monofunctional (meth)acrylate having an aromatic ringskeleton exhibits excellent curing properties, abrasion resistance, andphotopolymerization initiator solubility.

The monofunctional (meth)acrylate having an aromatic ring skeleton is acompound having an aromatic ring skeleton and also one (meth)acryloylgroup as a polymerizable functional group in one molecule. Examples ofthe monofunctional (meth)acrylate having an aromatic ring skeletoninclude, but not limited to, benzyl (meth)acrylate, phenoxyethyl(meth)acrylate, alkoxylated 2-phenoxyethyl (meth)acrylate, ethoxylatednonylphenyl (meth)acrylate, alkoxylated nonylphenyl (meth)acrylate,p-cumylphenol EO-modified (meth)acrylate, and 2-hydroxy-3-phenoxypropyl(meth)acrylate. Examples of commercially available monofunctional(meth)acrylate having an aromatic ring skeleton include Viscoat #192(trade name of phenoxyethyl acrylate manufactured by Osaka OrganicChemical Industry Ltd.); and SR340 (phenoxyethyl methacrylate), SR339A(phenoxyethyl acrylate), SR504 (ethoxylated nonylphenyl acrylate), CD614(alkoxylated nonylphenyl acrylate), and CD9087 (alkoxylated2-phenoxyethyl acrylate) (trade names of products manufactured bySartomer Company Inc.).

Among these compounds, preferred are compounds represented by thefollowing Formula (II) or (III):CH₂═CR⁴—COOR⁵—Ar  (II)CH₂═CR⁴—COO—Ar  (III)(R⁴ in Formulae (II) and (III) represents a hydrogen atom or a methylgroup; Ar in Formula (II) represents an aromatic ring skeleton having atleast one aryl group where a carbon atom constituting the aryl group isa monovalent organic residue binding to the group represented by R⁵; R⁵represents a divalent organic residue having 1 to 4 carbon atoms; and Arin Formula (III) represents an aromatic ring skeleton having at leastone aryl group where a carbon atom constituting the aryl group is amonovalent organic residue binding to —COO— in the formula).

In Formula (II), the organic residue represented by R⁵ is preferably anoptionally substituted linear, branched, or circular alkylene grouphaving 1 to 4 carbon atoms or an optionally substituted alkylene grouphaving 1 to 4 carbon atoms and an oxygen atom involved in an ether bondand/or an ester bond in its structure. Among them, more preferred arealkylene groups having 1 to 4 carbon atoms, such as an ethylene group,an n-propylene group, an isopropylene group, and a butylene group; andalkylene group having 1 to 4 carbon atoms and an oxygen atom involved inan ether bond in its structure, such as an oxyethylene group, anoxy-n-propylene group, an oxyisopropylene group, and an oxybutylenegroup. When the organic residues have substituents, examples of thesubstituents include, but not limited to, carboxyl groups, alkoxygroups, hydroxyl groups, and halo groups. In the case of a substituentcontaining a carbon atom, the carbon atom is counted as the carbon atomof the organic residue.

Ar (aromatic ring skeleton) in Formulae (II) and (III) includes at leastone aryl group. Examples of the aryl group include, but not limited to,phenyl groups and naphthyl groups. The number of the aryl group is atleast one and preferably one or two. The aryl group may be substitutedon a carbon atom constituting the group excluding the carbon atombinding to the organic residue represented by R⁵ in Formula (II), thecarbon atom binding to —COO— in Formula (III), and the carbon atomsbinding between aryl groups in the case of Ar having two or more arylgroups. When the aryl group is substituted, the number of thesubstituents is at least one, preferably one or two, for each arylgroup. Examples of the substituent include, but not limited to, linear,branched, or circular alkylene and alkoxy groups having 1 to 10 carbonatoms, carboxyl groups, halo groups, and hydroxyl groups.

Among them, phenoxyethyl (meth)acrylate, more preferably phenoxyethylacrylate, exhibits good compatibility with additives such as thephotopolymerization initiator, can decrease viscosity and odor, providesfurther excellent reactivity (curing property), and is thereforepreferred.

The content of the monofunctional (meth)acrylate having an aromatic ringskeleton is 5 to 40% by mass based on the total mass of the inkcomposition (100% by mass). A content of 5% by mass or more can provideexcellent curing properties and photopolymerization initiator solubilityand satisfactory abrasion resistance. A content of 40% by mass or lessprovides excellent adhesion and abrasion resistance and alsosatisfactory curing properties. In order to obtain higherphotopolymerization initiator solubility, the content is preferably 10to 40% by mass, more preferably 12 to 33% by mass.

Polymerizable Compound Other than the Above

In addition to the vinyl ether group-containing (meth)acrylic esters andthe monofunctional (meth)acrylate having an aromatic ring skeleton, theink composition may further contain various known monomers andoligomers, such as monofunctional, difunctional, and tri- ormore-functional monomers and oligomers (hereinafter, referred to as“other polymerizable compound”). Examples of the monomer includeunsaturated carboxylic acids (e.g., (meth)acrylic acid, itaconic acid,crotonic acid, isocrotonic acid, and maleic acid, salts and estersthereof), urethanes, amides and anhydrides thereof, acrylonitrile,styrene, various unsaturated polyesters, unsaturated polyethers,unsaturated polyamides, and unsaturated urethanes. Examples of theoligomer include oligomers formed from the monomers mentioned above(e.g., linear acrylic oligomers), epoxy (meth)acrylate, oxetane(meth)acrylate, aliphatic urethane (meth)acrylate, aromatic urethane(meth)acrylate, and polyester (meth)acrylate.

As the other monofunctional monomer or multifunctional monomer, anN-vinyl compound may be used. Examples of the N-vinyl compound includeN-vinyl formamide, N-vinyl carbazole, N-vinyl acetamide, N-vinylpyrrolidone, N-vinylcaprolactam, and acryloylmorpholine, and derivativesthereof.

Among other polymerizable compounds, ester of (meth)acrylic acid, i.e.,(meth)acrylate is preferable.

Among the (meth)acrylates mentioned above, examples of themonofunctional (meth)acrylate excluding those having an aromatic ringskeleton include isoamyl (meth)acrylate, stearyl (meth)acrylate, lauryl(meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, isomyristyl(meth)acrylate, isostearyl (meth)acrylate, 2-ethylhexyl-diglycol(meth)acrylate, 2-hydroxybutyl (meth)acrylate, butoxyethyl(meth)acrylate, ethoxydiethylene glycol (meth)acrylate,methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol(meth)acrylate, methoxypropylene glycol (meth)acrylate, isobornyl(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, lactone-modified flexible (meth)acrylate,tetrahydrofurfuryl (meth)acrylate, t-butylcyclohexyl (meth)acrylate,dicyclopentanyl (meth)acrylate, and dicyclopentenyloxyethyl(meth)acrylate.

Among the (meth)acrylates mentioned above, examples of difunctional(meth)acrylate include triethylene di(meth)acrylate, tetraethyleneglycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,dipropylene glycol di(meth)acrylate, tripropylene glycoldi(meth)acrylate, polypropylene glycol di(meth)acrylate, 1,4-butanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate,dimethylol-tricyclodecane di(meth)acrylate, EO (ethylene oxide) adductdi(meth)acrylate of bisphenol A, PO (propylene oxide) adductdi(meth)acrylate of bisphenol A, hydroxypivalic acid neopentyl glycoldi(meth)acrylate, and polytetramethylene glycol di(meth)acrylate.

Among the (meth)acrylates mentioned above, examples of tri- ormore-functional (meth)acrylate include trimethylolpropanetri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate,pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol hexa(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, glycerin propoxy tri(meth)acrylate,caprolactone-modified trimethylolpropane tri(meth)acrylate,pentaerythritolethoxy tetra(meth)acrylate, and caprolactam-modifieddipentaerythritol hexa(meth)acrylate.

Among these compounds, in order to further increase the strength of acoating film and obtain further excellent abrasion resistance, the otherpolymerizable compound preferably contains tri- or more-functional(meth)acrylate, i.e., a tri- or more-functional (meth)acrylic monomer,more preferably a trifunctional (meth)acrylic monomer.

In the case where the ink composition of the embodiment contains apolymerizable compound in addition to the vinyl ether group-containing(meth)acrylic esters and the monofunctional (meth)acrylate having anaromatic ring skeleton, the content of the polymerizable compound ispreferably 3 to 30% by mass, more preferably 5 to 20% by mass, based onthe total mass (100% by mass) of the ink composition. Within the contentrange above, the solubility of the additives is excellent, and a coatingfilm having high toughness, heat resistance, and chemical resistance canbe formed.

In particular, when the ink composition further contains a trifunctional(meth)acrylic monomer, the content of the trifunctional (meth)acrylicmonomer is preferably 3 to 22% by mass, more preferably 3 to 17% bymass, based on the total mass (100% by mass) of the ink composition.Within the content range above, the solubility of the additives such asthe photopolymerization initiator is further excellent, and theviscosity can be further decreased.

The polymerizable compounds may be used alone or in a combination of twoor more thereof.

Photopolymerization Initiator

The photopolymerization initiator contained in the ink composition ofthe embodiment allows an ink present on a recording medium surface tocure by photopolymerization under ultraviolet irradiation to achieveprinting. In radiation, ultraviolet (UV) is excellent in safety, and thelight source lamp thereof is inexpensive. The photopolymerizationinitiator may be any one that generates active species such as radicalsand cations by light (ultraviolet) energy and thereby initiatespolymerization of the polymerizable compound. For example, aphoto-radial polymerization initiator or a photo-cation polymerizationinitiator can be used. In particular, the photo-radial polymerizationinitiator is preferred.

Examples of the photo-radial polymerization initiator include aromaticketones, acylphosphine oxide compounds, aromatic onium salt compounds,organic peroxides, thio compounds (e.g., thioxanthone compounds andthiophenyl group-containing compounds), hexaarylbiimidazole compounds,ketoxime ester compounds, borate compounds, azinium compounds,metallocene compounds, active ester compounds, compounds havingcarbon-halogen bonds, and alkylamine compounds.

In particular, the acylphosphine oxide compound can make the curingproperties of an ink satisfactory and is therefore preferred. Morepreferred is to contain both the acylphosphine oxide compound and thethioxanthone compound.

Specific examples of the photo-radial polymerization initiator includeacetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenylketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole,3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone,4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether,benzoin ethyl ether, benzyl dimethyl ketal,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one,2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone,diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide,2,4-diethylthioxanthone, andbis-(2,6-dimethoxybenzoyl)-2,4,4-tiemethylpentylphosphine oxide.

Examples of commercially available photo-radial polymerization initiatorinclude IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethan-1-one), IRGACURE184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173(2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one),IRGACURE 127(2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl]-2-methyl-propan-1-one}),IRGACURE 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one),IRGACURE 369(2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), IRGACURE379(2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone),DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), IRGACURE 784(bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium),IRGACURE OXE 01 (1,2-octanedione, 1-[4-(phenylthio)-,2-(O-benzoyloxime)]), IRGACURE OXE 02 (ethanone,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime)),IRGACURE 754 (oxyphenylacetic acid, 2-[2-oxo-2-phenylacetoxyethoxy]ethylester, and a mixture of oxyphenylacetic acid and2-(2-hydroxyethoxy)ethyl ester) (each manufactured by BASF), KAYACUREDETX-S (2,4-diethylthioxanthone) (manufactured by Nippon Kayaku Co.,Ltd.), Lucirin TPO, LR8893, and LR8970 (each manufactured by BASF), andUbecryl P36 (manufactured by UCB).

The photopolymerization initiators may be used alone or in a combinationof two or more thereof.

In order to sufficiently accelerate ultraviolet curing speed and, at thesame time, to avoid insufficient dissolution of the photopolymerizationinitiator and avoid coloring due to the photopolymerization initiator,the content of the photopolymerization initiator is preferably 9% bymass or more, more preferably 9 to 17% by mass, based on the total mass(100% by mass) of the ink composition.

When the photopolymerization initiator includes the acylphosphine oxidecompound, in order to obtain a sufficiently high curing speed, inparticular, in curing with an LED (350 to 420 nm) and to thereby obtainfurther excellent curing properties, the content of the acylphosphineoxide compound is preferably 7% by mass or mass, more preferably 7 to15% by mass, and in order to obtain further excellent curing properties,most preferably 10 to 15% by mass, based on the total mass (100% bymass) of the ink composition.

Polymerization Accelerator

The ink composition of the embodiment may contain a polymerizationaccelerator. Examples of the polymerization accelerator include, but notlimited to, p-dimethylaminobenzoic acid esters and amino (meth)acrylate.

Among them, amino (meth)acrylate has excellent reactivity, inparticular, can make curing properties of a thin film satisfactory, andis therefore preferred. The amino (meth)acrylate is a compound having atleast one amino group and at least one (meth)acryloyl group. Preferredexamples of the amino (meth)acrylate include, but not limited to,compounds obtained by reaction of an amine compound and at least one ofmonofunctional (meth)acrylate, difunctional (meth)acrylate, and tri- ormore-functional (meth)acrylate.

Examples of commercially available amino (meth)acrylate include CN371(trade name of a compound containing two amino groups and two acryloylgroups manufactured by Sartomer Company Inc.); EBECRYL 7100 (trade nameof a compound containing two amino groups and two acryloyl groupsmanufactured by Cytech, Inc.); and CN386 (compound containing two aminogroups and one acryloyl group), CN372 (compound containing one aminogroup and one acryloyl group), CN373 (compound containing one aminogroup and two acryloyl groups), CN383 (compound containing one aminogroup and one acryloyl group), and CN374 (compound containing two aminogroups and one acryloyl group) (trade names of products manufactured bySartomer Company Inc.).

The polymerization accelerators may be used alone or in a combination oftwo or more thereof.

The content of the polymerization accelerator, in particular, the amino(meth)acrylate is preferably 2 to 22% by mass based on the total mass(100% by mass) of the ink composition. Within this content range, thethin film curing properties are further improved. The “thin film” in thethin film curing properties is a film having a thickness of 3 μm orless, more specifically, a film having a thickness of 1 to 2 μm.

Polymerization Inhibitor

The ink composition of the embodiment may contain a polymerizationinhibitor. Examples of the polymerization inhibitor include, but notlimited to, phenol compounds such as p-methoxyphenol, cresol,t-butylcatechol, di-t-butyl paracresol, hydroquinone monomethyl ether,α-naphthol, 3,5-di-t-butyl-4-hydroxytoluene, 2,2′-methylenebis(4-methyl-6-t-butylphenol), 2,2′-methylenebis(4-ethyl-6-butylphenol), and 4,4′-thiobis(3-methyl-6-t-butylphenol);quinone compounds such as p-benzoquinone, anthraquinone, naphthoquinone,phenanthraquinone, p-xyloquinone, p-toluquinone, 2,6-dichloroquinone,2,5-diphenyl-p-benzoquinone, 2,5-diacetoxy-p-benzoquinone,2,5-dicaproxy-p-benzoquinone, 2,5-diacyloxy-p-benzoquinone,hydroquinone, 2,5-di-butylhydroquinone, mono-t-butylhydroquinone,monomethylhydroquinone, and 2,5-di-t-amylhydroquinone; amine compoundssuch as phenyl-β-naphthylamine, p-benzylaminephenol, di-β-naphthylparaphenyldiamine, dibenzyl hydroxylamine, phenyl hydroxylamine, anddiethyl hydroxylamine; nitro compounds such as dinitrobenzene,trinitrotoluene, and picric acid; oxime compounds such as quinonedioxime and cyclohexanone oxime; and sulfur compounds such asphenothiazine.

The polymerization inhibitors may be used alone or in a combination oftwo or more thereof. The amount of the polymerization inhibitor is notparticularly limited, and an approximate amount thereof may be added.

Coloring Material

The ink composition of the embodiment further contains a coloringmaterial. The coloring material can be a pigment and/or a dye.

Pigment

In the embodiment, the use of a pigment as the coloring material canincrease the light resistance of the ink composition. The pigment may bean inorganic pigment or an organic pigment.

As the inorganic pigment, for example, carbon blacks (e.g., C.I. PigmentBlack 7), such as furnace black, lamp black, acetylene black, andchannel black; iron oxide; and titanium oxide can be used.

Examples of the organic pigment include azo pigments, such as insolubleazo pigments, condensed azo pigments, azo lake, and chelate azopigments; polycyclic pigments, such as phthalocyanine pigments, peryleneand perinone pigments, anthraquinone pigments, quinacridone pigments,dioxane pigments, thioindigo pigments, isoindolinone pigments, andquinophthalone pigments; dye chelates (e.g., basic dye chelates and aciddye chelates); dye lakes (e.g., basic dye lakes and acid dye lakes); andnitro pigments, nitroso pigments, aniline black, and daylightfluorescent pigments.

More specifically, examples of the carbon black used in black inksinclude No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7,MA8, MA100, and No. 2200B (trade names of products manufactured byMitsubishi Chemical Corporation); Raven 5750, Raven 5250, Raven 5000,Raven 3500, Raven 1255, and Raven 700 (trade names of productsmanufactured by Carbon Columbia); Regal 400R, Regal 330R, Regal 660R,Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch1000, Monarch 1100, Monarch 1300, and Monarch 1400 (trade names ofproducts manufactured by CABOT JAPAN K.K.); and Color Black FW1, ColorBlack FW2, Color Black FW2V, Color Black FW18, Color Black FW200, ColorBlack S150, Color Black 5160, Color Black 5170, Printex 35, Printex U,Printex V, Printex 140U, Special Black 6, Special Black 5, Special Black4A, and Special Black 4 (trade names of products manufactured byDegussa).

Examples of the pigment used in white inks include C.I. Pigment White 6,18, and 21.

Examples of the pigment used in yellow inks include C.I. Pigment Yellow1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55,65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114,117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172,and 180.

Examples of the pigment used in magenta inks include C.I. Pigment Red 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23,30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112,114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177,178, 179, 184, 185, 187, 202, 209, 219, 224, and 245; and C.I. PigmentViolet 19, 23, 32, 33, 36, 38, 43, and 50.

Examples of the pigment used in cyan inks include C.I. Pigment Blue 1,2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, and 66;and C.I. Vat Blue 4 and 60.

Examples of the pigment other than magenta, cyan, and yellow pigmentsinclude C.I. Pigment Green 7 and 10; C.I. Pigment Brown 3, 5, 25, and26; and C.I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38,40, 43, and 63.

The pigments may be used alone or in a combination of two or morethereof.

Dye

In the embodiment, the coloring material may be a dye. Any dye, such asacid dyes, direct dyes, reactive dyes, and basic dyes, can be used.Examples of the dye include C.I. Acid Yellow 17, 23, 42, 44, 79, and142; C.I. Acid Red 52, 80, 82, 249, 254, and 289; C.I. Acid Blue 9, 45,and 249; C.I. Acid Black 1, 2, 24, and 94; C.I. Food Black 1 and 2; C.I.Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, and 173;C.I. Direct Red 1, 4, 9, 80, 81, 225, and 227; C.I. Direct Blue 1, 2,15, 71, 86, 87, 98, 165, 199, and 202; C.I. Direct Black 19, 38, 51, 71,154, 168, 171, and 195; C.I. Reactive Red 14, 32, 55, 79, and 249; andC.I. Reactive Black 3, 4, and 35.

The dyes may be used alone or in a combination of two or more thereof.

The content of the coloring material is preferably 1 to 20% by massbased on the total mass (100% by mass) of the ink composition. Withinthe content range, satisfactory color-developing properties can beobtained, and prevention of curing of a coating film due to lightabsorption by the coloring material itself can be decreased.

Dispersant

When the ink composition of the embodiment contains a pigment, the inkcomposition may further contain a dispersant for well dispersing thepigment. Any dispersant can be used. For example, a dispersant that iscommonly used for preparing a pigment-dispersed liquid, such as apolymer dispersant, can be used. Specific examples of such a dispersantinclude those of which main component is at least one selected frompolyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers,acrylic polymers and copolymers, polyesters, polyamides, polyimides,polyurethanes, amino polymers, silicon-containing polymers,sulfur-containing polymers, fluorine-containing polymers, and epoxyresins. Examples of commercially available polymer dispersants includeAjisper series (trade name) manufactured by Ajinomoto Fine-Techno,Solsperse series (e.g., Solsperse 36000 (trade name) available fromAvecia Co.), Disperbyk series (trade name) manufactured by BYK Chemie,and Disparlon series (trade name) manufactured by Kusumoto Chemicals.

The dispersants may be used alone or in a combination of two or morethereof. The amount of the dispersant is not particularly limited, andan approximate amount thereof may be added.

Slipping Agent

The ink composition of the embodiment may further contain a slippingagent (surfactant). Any slipping agent can be used. For example,silicone surfactants such as polyester-modified silicone andpolyether-modified silicone can be used. In particular,polyether-modified polydimethylsiloxane and polyester-modifiedpolydimethylsiloxane are preferred. Specific examples thereof includeBYK-347, BYK-348, BYK-UV3500, 3510, 3530, and 3570 (each manufactured byBYK Chemie).

The slipping agents may be used alone or in a combination of two or morethereof. The amount of the slipping agent is not particularly limited,and an approximate amount thereof may be added.

Other Additives

The ink composition of the embodiment may contain additives (components)in addition to the above-described additives. Such components are notparticularly limited. For example, generally known penetrationaccelerator and wetting agent (moisturizing agent) and other additivescan be used. Examples of the other additive include generally knownfixing agent, antifungal agent, preservative, antioxidant, UV absorber,chelating agent, pH adjuster, and thickener.

Physical Properties of Photocurable Ink Jet Recording Ink Composition

The ink composition of the embodiment preferably has a viscosity at 25°C. of 5 to 15 mPa·s.

The ink composition can be cured by irradiation with ultraviolet lighthaving an emission peak wavelength in the range of preferably 350 to 420nm, more preferably 360 to 400 nm. The ink composition is preferablycured by irradiation with a UV energy of 400 mJ/cm² or less, morepreferably 300 mJ/cm² or less. The use of such an ink composition allowsformation of an image at low cost.

Thus, according to the embodiment, it is possible to provide aphotocurable ink jet recording ink composition that has excellent curingproperties, adhesion, and photopolymerization initiator solubility.Furthermore, the ink composition containing a predetermined amount ofthe vinyl ether group-containing (meth)acrylic esters, which have apredetermined structure including both a vinyl group and a (meth)acrylicgroup in one molecule, can have a lower viscosity and less odor and skinirritation and have excellent reactivity and adhesion. On the otherhand, the ink composition containing a predetermined amount of themonofunctional (meth)acrylate having an aromatic ring skeleton, whichhas both an aromatic ring and a (meth)acrylic group in one molecule, canhave a low viscosity and have excellent reactivity andphotopolymerization initiator solubility.

Recording Medium

The ink composition of the embodiment is discharged on a recordingmedium by a recording method described below to form a recorded matter.The recording medium may be absorbable or nonabsorbable. The recordingmethod of the embodiment described below can be widely applied tovarious recording media exhibiting highly different degrees ofabsorbability, i.e., from non-absorbing media into which aqueous inkhardly permeates to absorbing media into which aqueous ink easilypermeates. In the case of applying the ink composition to anon-absorbing recording medium, for example, a drying step may berequired after curing the ink composition by exposure to ultravioletlight.

Any absorbing recording medium can be used, and examples thereof includeplain paper such as electrophotographic paper highly absorbing aqueousinks, ink jet paper (special paper for ink jet printing and having anink absorbing layer containing silica particles or alumina particles oran ink absorbing layer made of a hydrophilic polymer such as polyvinylalcohol (PVA) or polyvinyl pyrrolidone (PVP)), and paper showingrelatively low absorbability for aqueous inks and used in ordinaryoffset printing, such as art paper, coated paper, and cast-coated paper.

Any non-absorbing recording medium can be used, and examples thereofinclude films, sheets, and plates of plastics such as polyvinyl chloride(PVC), polyethylene, polypropylene, and polyethylene terephthalate(PET); plates of metals such as iron, silver, copper, and aluminum;metal plates coated with such various metals by vapor deposition;plastic films; and plates of alloys such as stainless steel and brass.

Recording Method

An embodiment of the invention relates to a recording method. Thephotocurable ink jet recording ink composition according to theembodiment described above can be used in the recording method of thisembodiment. The recording method can be applied to an ink jet system.The recording method includes a discharging step of discharging theabove-described ink composition onto a recording medium; and a curingstep of curing the ink composition discharged in the discharging step byirradiating the ink composition with ultraviolet light. The inkcomposition thus cured on the recording medium forms a coating film(cured film).

Discharging Step

In the discharging step, an ink composition is discharged onto arecording medium so that the ink composition adheres to the recordingmedium. The ink composition at the time of being discharged preferablyhas a viscosity of 5 to 30 mPa·s. In the case of an ink compositionhaving such a viscosity at room temperature or in a non-heated state,the ink composition may be discharged at room temperature or withoutbeing heated. In such a case, the temperature of the ink at the time ofbeing discharged is preferably 20 to 30° C. Alternatively, an inkcomposition may be heated to a predetermined temperature to adjust theviscosity to a proper level and may be then discharged. Thus,satisfactory discharge stability is achieved.

The photocurable ink jet recording ink composition of the embodiment hasa higher viscosity than those of ordinary aqueous ink compositions. Theviscosity therefore largely varies depending on changes in temperaturewhen the ink composition is discharged. The change in viscosity of theink highly affects the sizes of droplets and the droplet-dischargingspeed, which may cause deterioration in image quality. Accordingly, itis preferred to maintain the temperature of the ink at the time ofdischarging as constant as possible.

Curing Step

Subsequently, the ink composition discharged and adhering to therecording medium is cured by light (ultraviolet) irradiation in thecuring step. This is caused by that the photopolymerization initiatorcontained in the ink composition is decomposed by ultravioletirradiation to generate initiation species such as radicals, acids, orbases and that polymerization of the polymerizable compound isaccelerated by the function of the initiation species, or is caused bythat polymerization of the polymerizable compound starts by ultravioletirradiation. If the ink composition contains a sensitizing dye togetherwith the photopolymerization initiator, the sensitizing dye in thesystem absorbs ultraviolet light and thereby changes to an excitedstate, which accelerates decomposition of the photopolymerizationinitiator by contact therewith. As a result, more sensitive curingreaction is achieved.

As the ultraviolet light source, a mercury lamp or a gas/solid laser ismainly used. As light sources for curing photocurable ink jet recordingink compositions, mercury lamps and metal halide lamps are widely used.However, from the viewpoint of environmental protection, it is highlydesired to be mercury-free, and replacement by GaN-based semiconductorultraviolet light emitting devices is very useful industrially andenvironmentally. In addition, ultraviolet light-emitting diodes(UV-LEDs) and ultraviolet light-emitting laser diodes (UV-LDs) aresmall-sized and have long life and high efficiency and are low in cost,and are therefore expected as light sources for photocurable ink jetrecording. Among them, UV-LEDs are preferred.

A UV-LED having an emission peak wavelength in a range of 350 to 420 nm(more preferably 360 to 400 nm) can easily increase the output and istherefore suitable for a recording method using a photocurable ink jetrecording ink composition that can be cured by irradiation with anenergy of preferably 400 mJ/cm² or less, more preferably 300 mJ/cm² orless. In such a case, a high printing speed can be obtained at low cost.Such an ink composition can be obtained by containing aphotopolymerization initiator that is decomposed by exposure toultraviolet light having a wavelength in the above-mentioned rangeand/or a polymerizable compound that starts polymerization by exposureto ultraviolet light having a wavelength in the above-mentioned range.

Thus, according to the embodiment, it is possible to provide asatisfactory recording method using a photocurable ink jet recording inkcomposition that has excellent curing properties, adhesion, andsolubility of a photopolymerization initiator.

EXAMPLES

The embodiments of the first invention will now be more specificallydescribed by non-limiting examples.

Components

Components used in the following Examples and Comparative Examples areas follows.

Polymerizable Compound:

VEEA (trade name of 2-(2-vinyloxyethoxy)ethyl acrylate manufactured byNippon Shokubai Co., Ltd., hereinafter abbreviated as “VEEA”)

APG-100 (trade name of dipropylene glycol diacrylate manufactured byShin-Nakamura Chemical Co., Ltd., hereinafter abbreviated as “DPGDA”)

IBXA (trade name of isobornyl acrylate manufactured by Osaka OrganicChemical Industry Ltd., hereinafter abbreviated as “IBXA”)

APG-200 (trade name of tripropylene glycol diacrylate manufactured byShin-Nakamura Chemical Co., Ltd., hereinafter abbreviated as “TPGDA”)

SR230 (diethylene glycol diacrylate manufactured by Sartomer CompanyInc., hereinafter abbreviated as “DEGDA”)

Viscoat #192 (trade name of phenoxyethyl acrylate manufactured by OsakaOrganic Chemical Industry Ltd., hereinafter abbreviated as “PEA”)

FA-BZA (trade name of benzyl acrylate manufactured by Hitachi ChemicalCompany, Ltd., hereinafter abbreviated as “BA”)

Photopolymerization Initiator:

IRGACURE 819 (trade name, manufactured by BASF, hereinafter abbreviatedas “819”)

DAROCUR TPO (trade name, manufactured by BASF, solid content: 100%,hereinafter abbreviated as “TPO”)

KAYACURE DETX-S (trade name, manufactured by Nippon Kayaku Co., Ltd.,hereinafter abbreviated as “DETX-S”)

Pigment:

Pigment Black 7 (carbon black) (Microlith Black C-K (trade name),manufactured by BASF, hereinafter abbreviated as “Black”)

Dispersant:

Solsperse 36000 (trade name, manufactured by Lubrizol, hereinafterabbreviated as “Sol36000”)

Examples 1 to 24

The components shown in the following tables were mixed in variouscompositions (unit: % by mass) shown in the tables, and the mixtureswere stirred with a high-speed water-cooled stirrer to obtain black inkcompositions.

TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 Polymerizable VEEA 20.0 20.0 10.030.0 20.0 10.0 30.0 10.0 40.0 5.0 compound DPGDA 65.0 35.0 30.0 30.0 5.05.0 5.0 65.0 30.0 30.0 IBXA TPGDA DEGDA PEA 30.0 45.0 25.0 60.0 70.050.0 10.0 15.0 50.0 BA Photopolymerization 819 6.0 6.0 6.0 6.0 6.0 6.06.0 6.0 6.0 6.0 initiator TPO 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0DETX-S 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Pigment Black 2.0 2.0 2.02.0 2.0 2.0 2.0 2.0 2.0 2.0 Dispersant Sol36000 1.0 1.0 1.0 1.0 1.0 1.01.0 1.0 1.0 1.0 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0100.0 100.0

TABLE 2 Example 11 12 13 14 15 16 17 18 19 20 21 22 23 24 PolymerizableVEEA 30.0 30.0 10.0 10.0 65.0 30.0 15.0 20.0 30.0 33.0 30.0 30.0 30.0compound DPGDA 3.0 70.0 30.0 10.0 20.0 35.0 30.0 30.0 30.0 IBXA 30.025.0 25.0 33.0 25.0 30.0 TPGDA 30.0 15.0 DEGDA 30.0 PEA 25.0 25.0 72.05.0 55.0 10.0 25.0 35.0 25.0 25.0 BA 30.0 Photopolymerization 819 6.06.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 initiator TPO 4.04.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 DETX-S 2.0 2.0 2.02.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Pigment Black 2.0 2.0 2.02.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Dispersant Sol36000 1.0 1.0 1.0 1.01.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Total 100.0 100.0 100.0 100.0 100.0100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0Evaluation Items1. Curing Property

The respective nozzle arrays of an ink jet printer, PX-G5000 (tradename, manufactured by Seiko Epson Corporation), were filled with thephotocurable ink compositions prepared above. A solid pattern image(recording resolution: 720×720 dpi) was printed on a PET film (Rumirer125E20 (trade name), manufactured by Toray Industries, Inc.) underordinary temperature and ordinary pressure with a dot diameter of middleso that the printed matter has a thickness of 6 μm. After printing, thesolid pattern image was cured by irradiation with 200 mJ/cm² ofultraviolet light having a wavelength of 395 nm at an irradiationintensity of 60 mW/cm² using a UV-LED (Firefly, manufactured by Phoseon)in an ultraviolet irradiation device. Thus, recorded matters where solidpattern images were printed on PET films were produced. The solidpattern image is an image that has recorded the dot for every pixel, thepixel is a minimum recording unit region defined by recoding resolution.

The irradiation energy [mJ/cm²] was determined as the product obtainedby multiplying the irradiation intensity [mW/cm²] on the surfaceirradiated with light from a light source by the irradiation durationtime [s]. The irradiation intensity was measured using an ultravioletray intensity meter, UM-10, and a receptor head, UM-400 (bothmanufactured by Konica Minolta Sensing, Inc.).

The curing properties of coating films were evaluated using theirradiation energy at the time of tack-free as an index. Whether acoating film was in a tack-free state or not was determined based on thefollowing conditions: whether an ink adhered to a cotton swab or not andwhether a cured ink material on a recording medium was abraded or not.When the ink did not adhere to a cotton swab and also the cured inkmaterial on a recording medium was not abraded, the coating film wasdetermined to be in a tack-free state. The cotton swab used was Johnsoncotton swab manufactured by Johnson & Johnson. Each coating film wasrubbed with the cotton swab back and forth 10 times under a load of 100g.

The evaluation results are shown in the following tables, and theevaluation criteria are as follows:

AA: irradiation energy at tack-free time was 150 mJ/cm² or less,

A: irradiation energy at tack-free time was higher than 150 mJ/cm² and200 mJ/cm² or less,

B: irradiation energy at tack-free time was higher than 200 mJ/cm² and300 mJ/cm² or less, and

C: irradiation energy at tack-free time was higher than 300 mJ/cm² and400 mJ/cm² or less.

2. Curing Wrinkles

The respective nozzle arrays of an ink jet printer, PX-G5000 (tradename, manufactured by Seiko Epson Corporation), were filled with thephotocurable ink compositions prepared above. A solid pattern image(recording resolution: 720×720 dpi) was printed on a PET film (Rumirer125E20 (trade name), manufactured by Toray Industries, Inc.) underordinary temperature and ordinary pressure with a dot diameter of middleso that the printed matter has a thickness of 6 μm. After printing, thesolid pattern image was cured by irradiation with 200 mJ/cm² ofultraviolet light having a wavelength of 395 nm at an irradiationintensity of 60 mW/cm² using a UV-LED in an ultraviolet irradiationdevice. If the curing of a sample did not reach a tack-free state, theirradiation was continued until the sample reached a tack-free state.

Thus, recorded matters where solid pattern images were printed on PETfilms were produced.

The method of confirming a tack-free state and solid pattern images andthe measurement and calculation of irradiation energies and irradiationintensities are the same as those in the “curing properties” evaluation.

The degrees of occurrence of curing wrinkles were evaluated by visuallyobserving the surface of each solid pattern image after completion ofcuring.

The evaluation results are shown in the following tables, and theevaluation criteria are as follows:

A: no wrinkles were observed on the image surface after curing,

B: a few wrinkles were observed on the image surface after curing, andthe surface roughness Rq was 4 or less, and

C: wrinkles were observed on the image surface after curing, and thesurface roughness Rq was higher than 4.

3. Adhesion Evaluation by Peeling Test

Transparent adhesive tape (width: 25±1 mm) was put on a coating film ofeach image formed by solid printing under the same conditions (printingand curing conditions) as those in the “curing wrinkles” evaluation. Thetape was sufficiently rubbed with a finger so that the coating film canbe seen through the tape. Within 5 min from the adhesion, the tape wascertainly peeled off at an angle of about 60 degrees with taking 0.5 to1.0 sec.

The evaluation results are shown in the following tables, and theevaluation criteria are as follows:

A: no peeling of coating film was observed, and

B: peeling of coating film was observed.

4. Adhesion Evaluation by Cutting Test

In accordance with JIS K-5600-5-6 (ISO 2409) (Testing methods forpaints—Part 5: Mechanical property of film—Section 6: Adhesion test(Cross-cut test), adhesion between a PET film (Rumirer 125E20 (tradename), manufactured by Toray Industries, Inc.) and an image formed bysolid printing under the same conditions (printing and curingconditions) as those in the “curing wrinkles” evaluation was evaluated.The cross-cut test will now be described.

As cutting tools, a single blade cutter (commonly commercially availablecutter) and a guide for making cuts at equal intervals with the singleblade cutter were prepared.

First, six cuts were made in a recorded matter with the blade of thecutter vertically put on the coating film. After making the six cuts,the blade was turned by 90 degrees and made another six cuts so as to beorthogonal to the six cuts previously made.

About 75 mm of transparent adhesive tape (width: 25±1 mm) was attachedto the coating film at the portion provided with the cuts in a latticeform. The tape was sufficiently rubbed with a finger so that the coatingfilm can be seen through the tape. Within 5 min from the adhesion, thetape was certainly peeled off at an angle of about 60 degrees withtaking 0.5 to 1.0 sec.

The evaluation results are shown in the following tables, and theevaluation criteria are as follows:

A: peeling was observed in less than 5% of the lattices,

B: peeling was observed in 5% or more and less than 35% of the lattices,and

C: peeling was observed in 35% or more of the lattices.

5. Abrasion Resistance

In accordance with JIS K5701 (ISO 11628) (regulation for methods oftesting ink, color-developing sample, and printed matter used inplanographic printing), abrasion resistance was evaluated using aGakushin-type rubbing fastness tester (manufactured by Tester SangyoCo., Ltd.). A cannequin was placed on the surface of a recorded matter(solid printed matter) obtained by solid printing under the sameconditions (printing and curing conditions) as those in the “curingwrinkles” evaluation. The surface was rubbed with the cannequin under aload of 500 g. Peeling off of cured surface of the recorded matter afterrubbing was compared by visual observation.

The evaluation results are shown in the following tables, and theevaluation criteria are as follows:

A: no stain was observed on the cannequin, and no peeling and scratchwere observed on the printed surface,

B: stain was observed on the cannequin, but no peeling and scratch wereobserved on the printed surface, and

C: stain was observed on the cannequin, and peeling and scratch wereobserved on the printed surface.

6. Storage Stability

Twenty-four milliliters of each of the ink compositions was put in a30-mL glass bottle and was left to stand at 60° C. for 1 week with lightshielding. An increase in viscosity of each ink by leaving to stand wascalculated from the viscosities before and after the leaving, andstorage stability of the ink was evaluated based on the increase.

The evaluation results are shown in the following tables, and theevaluation criteria are as follows:

A: the rate of increase in viscosity was less than 5%,

B: the rate of increase in viscosity was 5% or more and less than 10%,and

C: the rate of increase in viscosity was 10% or more.

7. Photopolymerization Initiator Solubility

Components excluding the pigment and the dispersant in each inkcomposition in the examples were sufficiently stirred at roomtemperature to prepare ink compositions not containing pigment.Subsequently, whether undissolved photopolymerization initiator waspresent or not was visually evaluated.

The evaluation results are shown in the following tables, and theevaluation criteria are as follows:

A: no undissolved photopolymerization initiator was observed, and

B: undissolved photopolymerization initiator was observed.

TABLE 3 Example 1 2 3 4 5 6 7 8 9 10 Curing property C A A AA AA A AA AAA B Curing wrinkle C A A A A A A A B A Adhesion Peeling A A A A A A A AA A Cutting A A A A B B B A B A Abrasion resistance A A A A A A A A A AStorage stability B A A A A A A A B A Polymerization B A A A A A A A A Ainitiator solubility

TABLE 4 Example 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Curingproperty C C B B C AA C B AA B A B A B Curing wrinkle C B B B B B B B AC B B A A Adhesion Peeling B A B A A A A B A A A A A B Cutting C B B A AB B B A A A B A C Abrasion B A B A A A B A A A A B A B resistanceStorage stability A A A A A B A A A B B A — — Polymerization A A A A A AA A A B B A — — initiator solubility

The results shown in the tables reveal that photocurable inkcompositions (examples 2 to 10, 13, 14, 16, 18, and 19) each containingvinyl ether group-containing (meth)acrylic esters represented by Formula(I), dipropylene glycol di(meth)acrylate, monofunctional (meth)acrylatehaving an aromatic ring skeleton, and a coloring material are superiorto other photocurable ink compositions in curing property, prevention ofcuring wrinkles, polymerization initiator solubility, adhesion, andabrasion resistance.

The ink compositions of examples 21 and 22 are examples not containingany coloring material. Though these ink compositions do not contain thedipropylene glycol di(meth)acrylate or the monofunctional (meth)acrylatehaving an aromatic ring skeleton, the curing properties are satisfactoryand occurrence of curing wrinkles is satisfactorily low. However, theseink compositions do not contain any coloring material and cannot betherefore applied to coloring of recording media.

The ink compositions of examples 23 and 24 are the same as those ofexamples 20 and 11, respectively. These ink compositions were evaluatedas in the ink compositions of examples 20 and 11 except that solidimages were irradiated with ultraviolet light having an irradiationintensity of 60 mW/cm² (irradiation intensity-measuring conditions arethe same as above), which was adjusted by attaching a filter to a metalhalide lamp (SMX-3500/F—OS, manufactured by Oak & Co., Ltd.). Thoughthese ink compositions do not contain the dipropylene glycoldi(meth)acrylate or the monofunctional (meth)acrylate having an aromaticring skeleton, the curing properties are satisfactory and occurrence ofcuring wrinkles is satisfactorily low. However, the recording media aredeformed by the heat from the metal halide lamp. On the other hand, thephotocurable ink compositions containing vinyl ether group-containing(meth)acrylic esters represented by Formula (I), dipropylene glycoldi(meth)acrylate, monofunctional (meth)acrylate having an aromatic ringskeleton, and a coloring material are recognized as ink compositionsexhibiting, in particular, excellent curing properties and sufficientlylow occurrence of curing wrinkles by irradiation with light from everylight sources. The storage stability and the polymerization initiatorsolubility of examples 23 and 24 are the same as those of examples 20and 11, respectively, and were therefore not evaluated.

In the ink composition (example 14) containing the monofunctional(meth)acrylate having an aromatic ring skeleton in a content of lessthan 10%, it takes a long time to dissolve the photopolymerizationinitiator.

The embodiments of the second invention will now be more specificallydescribed by non-limiting examples.

Components

Components used in the following Examples and Comparative Examples areas follows.

Vinyl Ether Group-Containing (Meth)Acrylic Esters:

VEEA (trade name of 2-(2-vinyloxyethoxy)ethyl acrylate manufactured byNippon Shokubai Co., Ltd., hereinafter abbreviated as “VEEA”)

Monofunctional (Meth)Acrylate Having an Aromatic Ring Skeleton:

Viscoat #192 (trade name of phenoxyethyl acrylate manufactured by OsakaOrganic Chemical Industry Ltd., hereinafter abbreviated as “PEA”)

FA-BZA (trade name of benzyl acrylate manufactured by Hitachi ChemicalCompany, Ltd., hereinafter abbreviated as “BZA”)

Other Polymerizable Compounds:

NK Ester A-TMPT (trade name of trimethylolpropane triacrylatemanufactured by Shin-Nakamura Chemical Co., Ltd., hereinafterabbreviated as “A-TMPT”)

IBXA (trade name of isobornyl acrylate manufactured by Osaka OrganicChemical Industry Ltd., hereinafter abbreviated as “IBXA”)

NK Ester APG-200 (trade name of tripropylene glycol diacrylatemanufactured by Shin-Nakamura Chemical Co., Ltd., hereinafterabbreviated as “3PGA”)

NK Ester APG-100 (trade name of dipropylene glycol diacrylatemanufactured by Shin-Nakamura Chemical Co., Ltd., hereinafterabbreviated as “2PGA”)

Photopolymerization Initiator:

IRGACURE 819 (trade name, manufactured by BASF, solid content: 100%,hereinafter abbreviated as “819”)

DAROCUR TPO (trade name, manufactured by BASF, solid content: 100%,hereinafter abbreviated as “TPO”)

KAYACURE DETX-S (trade name, manufactured by Nippon Kayaku Co., Ltd.,solid content: 100%, hereinafter abbreviated as “DETX-S”)

Polymerization Accelerator:

EBECRYL 7100 (trade name of amino acrylate manufactured by Cytech, Inc.,hereinafter abbreviated as “EBECRYL”)

Polymerization Inhibitor:

p-Methoxyphenol (manufactured by Tokyo Chemical Industry Co., Ltd.,hereinafter abbreviated as “MEHQ”)

Slipping Agent:

UV-3500 (trade name of a silicon-based surface conditioner manufacturedby BYK Chemie, hereinafter abbreviated as “V3500”)

Pigment:

Irgalite Blue Glvo (trade name of a cyan pigment (C.I. Pigment Blue15:4) manufactured by BASF, hereinafter abbreviated as “BLUE GLVO”)

Dispersant:

Solsperse 36000 (trade name, manufactured by Lubrizol, hereinafterabbreviated as “Sol36000”)

Examples 1 to 15 and Comparative Examples 1 to 5

The components shown in Tables 5 and 6 were mixed in variouscompositions (unit: % by mass) shown in the tables, and the mixtureswere stirred with a high-speed water-cooled stirrer to obtain cyan inkcompositions.

TABLE 5 Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple5 Example 6 Example 7 Example 8 Example 9 ple 10 Pigment BLUE GLVO 2.12.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 Dispersant SOL36000 0.5 0.5 0.5 0.50.5 0.5 0.5 0.5 0.5 0.5 Acrylic vinyl-containing VEEA 62.0 72.0 77.052.0 45.0 79.6 62.0 52.0 68.0 62.0 monomer Aromatic ring-containing PEA22.6 12.6 7.6 32.6 39.6 5.0 17.6 17.6 12.6 — monomer BZA — — — — — — — —— 22.6 Tri- or more-functional A-TMPT — — — — — — 5.0 15.0 — — monomerMonofunctional monomer IBXA — — — — — — — — — — Difunctional monomer3PGA — — — — — — — — — — 2PGA — — — — — — — — — — Polymerizationaccelerator EBECRYL — — — — — — — — 4.0 — Polymerization inhibitor MEHQ0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Slipping agent UV3500 0.2 0.20.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Photopolymerization 819 5.6 5.6 5.6 5.65.6 5.6 5.6 5.6 5.6 5.6 initiator TPO 4.8 4.8 4.8 4.8 4.8 4.8 4.8 4.84.8 4.8 DETX-S 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Total amount ofinitiators 12.4 12.4 12.4 12.4 12.4 12.4 12.4 12.4 12.4 12.4 Total 100.0100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

TABLE 6 Compar- Compar- Compar- Compar- Compar- Exam- Exam- Exam- Exam-Exam- ative ative ative ative ative ple 11 ple 12 ple 13 ple 14 ple 15Example 1 Example 2 Example 3 Example 4 Example 5 Pigment BLUE GLVO 2.12.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 Dispersant SOL36000 0.5 0.5 0.5 0.50.5 0.5 0.5 0.5 0.5 0.5 Acrylic vinyl-containing VEEA 62.0 62.0 47.047.0 45.0 40.0 83.0 62.0 38.0 — monomer Aromatic ring-containing PEA23.7 25.5 17.6 17.6 35.5 40.0 1.6 3.0 46.6 40.0 monomer BZA — — — — — —— — — — Tri- or more-functional A-TMPT — — 20.0 — — — — — — 14.6 monomerMonofunctional IBXA — — — — — 4.6 — 19.6 — — monomer Difunctionalmonomer 3PGA — — — — — — — — — 20.0 2PGA — — — — — — — — — 10.0Polymerization EBECRYL — — — 20.0 — — — — — — accelerator Polymerizationinhibitor MEHQ 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Slipping agentUV3500 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Photopolymerization 8194.5 5.0 5.6 5.6 7.0 5.6 5.6 5.6 5.6 5.6 initiator TPO 4.8 3.0 4.8 4.87.5 4.8 4.8 4.8 4.8 4.8 DETX-S 2.0 1.5 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0Total amount of initiators 11.3 9.5 12.4 12.4 16.5 12.4 12.4 12.4 12.412.4 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0Evaluation Items1. Viscosity

The viscosity of each of the ink compositions prepared above wasmeasured with a DVM-E-type rotational viscometer (manufactured by TokyoKeiki Inc.) under conditions of a temperature of 25° C. and a rotationalrate of 10 rpm. The evaluation results are shown in the followingtables, and the evaluation criteria are as follows:

A: 15 mPa·s or less,

B: higher than 15 mPa·s and 25 mPa·s or less, and

C: higher than 25 mPa·s.

2. Curing Property

The respective nozzle arrays of an ink jet recording apparatus havingpiezo-type ink jet nozzles were filled with the ink compositionsprepared above. A solid pattern image (recording resolution: 720×720dpi) was printed on a PVC sheet (Flontlite Grossy 120g (trade name),manufactured by Cooley) under ordinary temperature and ordinary pressureso that the printed matter has a thickness of 10 μm, and the solidpattern image was cured by irradiation with ultraviolet light having awavelength of 395 nm at an irradiation intensity of 1000 mW/cm² and adose of 200 mJ/cm² per pass using a UV-LED in an ultraviolet irradiationdevice mounted on the side of a carriage. Thus, recorded matters wheresolid pattern images were printed on PVC sheets were produced. The“solid pattern image” is an image that has recorded the dot for everypixel, the pixel is a minimum recording unit region defined by recodingresolution.

The irradiation energy [mJ/cm²] was determined as the product obtainedby multiplying the irradiation intensity [mW/cm²] on the surfaceirradiated with light from a light source by the irradiation durationtime [s]. The irradiation intensity was measured using an ultravioletray intensity meter, UM-10, and a receptor head, UM-400 (bothmanufactured by Konica Minolta Sensing, Inc.).

The curing properties of coating films were evaluated by the number ofpasses until surface tack disappeared. The “number of passes” refers tothe number of times of exposure of a recorded matter to ultravioletlight by moving the head toward the recorded matter and irradiating thelight to the coating film from the ultraviolet irradiation devicemounted on the head. The evaluation results are shown in the followingtables, and the evaluation criteria are as follows:

A: one pass,

B: two passes, and

C: three or more passes.

3. Adhesion

Recorded matters cured by light irradiation until surface tackdisappeared in the test of “2. Curing property” were used. In accordancewith JIS K-5600-5-6 (ISO 2409) (Testing methods for paints—Part 5:Mechanical property of film—Section 6: Adhesion test (Cross-cut test),adhesion was evaluated based on the following ranks A to E from theresults of a peeling test of recorded matters each having a coating filmprovided with cross-cuts and using adhesive tape. The cross-cut testwill now be described.

As cutting tools, a single blade cutter (commonly commercially availablecutter) and a guide for making cuts at equal intervals with the singleblade cutter were prepared.

First, six cuts were made in a recorded matter with the blade of thecutter vertically put on the coating film. After making the six cuts,the blade was turned by 90 degrees and made another six cuts so as to beorthogonal to the six cuts previously made.

About 75 mm of transparent adhesive tape (width: 25±1 mm) was attachedto the coating film at the portion provided with the cuts in a latticeform. The tape was sufficiently rubbed with a finger so that the coatingfilm can be seen through the tape. Within 5 min from the adhesion, thetape was certainly peeled off at an angle of about 60 degrees withtaking 0.5 to 1.0 sec.

The values of each rank are those obtained by rounding off thecalculated peeling rates to integer values. The evaluation results areshown in the following tables.

The evaluation criteria are as follows:

A: peeling rate was 0 to 5%,

B: peeling rate was 6 to 15%,

C: peeling rate was 16 to 35%,

D: peeling rate was 36 to 65%, and

E: peeling rate was 66 to 100%.

4. Abrasion Resistance

In accordance with JIS K5701, an abrasion resistance test was performedusing a Gakushin-type rubbing fastness tester (trade name, manufacturedby Tester Sangyo Co., Ltd.). That is, a cannequin was placed on thesurface of a recorded matter obtained in the test of “2. Curingwrinkles”, and the recorded surface was rubbed back and forth 100 timeswith the cannequin under a load of 500 g. Peeling-off and scratches ofthe recorded matter surface after rubbing were visually observed.

The evaluation results are shown in the following tables. The evaluationcriteria are as follows:

A: no stain was observed on the cannequin, and no peeling and scratchwere observed on the recorded surface,

B: stain was observed on the cannequin, but no peeling and scratch wereobserved on the recorded surface,

C: stain was observed on the cannequin, and linear peeling and scratchwere slightly observed on the recorded surface, and

D: stain was observed on the cannequin, and peeling and scratch wereobviously observed on the recorded surface.

5. Photopolymerization Initiator Solubility

Components excluding the pigment and the pigment-dispersing component ineach ink composition described above were sufficiently stirred.Subsequently, whether undissolved photopolymerization initiator waspresent or not was visually evaluated. The ink compositions notcontaining undissolved photopolymerization initiator were placed in athermostat chamber at 0° C. After 24 hours, the ink compositions weretaken out from the chamber, were warmed to room temperature, and werevisually observed again for whether the photopolymerization initiatorprecipitated or not.

The evaluation results are shown in the following tables. The evaluationcriteria are as follows:

A: no undissolved photopolymerization initiator and precipitation of thephotopolymerization initiator were observed after stirring at roomtemperature and after storage at 0° C.,

B: no undissolved photopolymerization initiator was observed afterstirring at room temperature, but precipitation of thephotopolymerization initiator was observed after storage at 0° C., and

C: undissolved photopolymerization initiator was observed after stirringat room temperature.

6. Thin-Film Curing Property

Thin-film curing properties of the ink compositions in Examples 1, 9,and 14 were evaluated as in the test of “2. Curing property” except thatthe printed matters were formed so as to have a thickness of 2 μminstead of 10 μm. The evaluation results are shown in the followingtables.

TABLE 7 Example Evaluation item Example 1 Example 2 Example 3 Example 4Example 5 Example 6 Example 7 Example 8 Example 9 10 Viscosity A A A A AA A A A A Curing property A A A A A A A A A A Adhesion A A A A B A A A AA Abrasion B B B B B B A A B B resistance Initiator solubility A A B A AB A A A A Thin-film curing B — — — — — — — A — property

TABLE 8 Example Example Example Example Example Comparative ComparativeComparative Comparative Comparative Evaluation item 11 12 13 14 15Example 1 Example 2 Example 3 Example 4 Example 5 Viscosity A A B B A AA A A C Curing property B B A A A B A C B B Adhesion A A A A B D A A D CAbrasion B B A B B B B B C A resistance Initiator solubility A A A A A AC C A A Thin-film curing — — — A — — — — — — property

The results shown in the tables reveal that the photocurable ink jetrecording ink composition (Examples) each containing vinyl ethergroup-containing (meth)acrylic esters having a predetermined structureand monofunctional (meth)acrylate having an aromatic ring skeleton inthe respective predetermined amounts are significantly superior to otherink compositions (Comparative Examples) at least in curing property,adhesion, and the solubility of photopolymerization initiator (initiatorsolubility).

What is claimed is:
 1. A photocurable ink composition comprisingpolymerizable compounds and a photopolymerization initiator, wherein thepolymerizable compounds include: vinyl ether group-containing(meth)acrylic esters represented by the following Formula (I):CH₂═CR¹—COOR²—O—CH═CH—R³  (I) (wherein, R¹ represents a hydrogen atom ora methyl group; R² represents a divalent organic residue having 2 to 20carbon atoms; and R³ represents a hydrogen atom or a monovalent organicresidue having 1 to 11 carbon atoms); dipropylene glycoldi(meth)acrylate; and monofunctional (meth)acrylate having an aromaticring skeleton, the ink composition includes a coloring material, whereinthe content of the monofunctional (meth)acrylate having an aromatic ringskeleton is 10 to 60% by mass based on the total mass of the inkcomposition, wherein the content of the dipropylene glycoldi(meth)acrylate is in the range of 3 to 20% by mass based on the totalmass of the ink composition, wherein the photopolymerization initiatoris an acylphosphine oxide compound and is contained in an amount between7 and 15% by mass based on the total mass of the ink composition, andwherein the content of the vinyl ether group-containing (meth)acrylicesters is in the range of 5 to 65% by mass based on the total mass ofthe ink composition.
 2. The photocurable ink composition according toclaim 1, wherein the content of the dipropylene glycol di(meth)acrylateis 5 to 25% by mass based on the total mass of the ink composition. 3.The photocurable ink composition according to claim 1, wherein thecontent of the vinyl ether group-containing (meth)acrylic esters is 10to 30% by mass based on the total mass of the ink composition.
 4. Thephotocurable ink composition according to claim 1, wherein thephotopolymerization initiator is an acylphosphine oxide compound and iscontained in an amount of 9 to 15% by mass based on the total mass ofthe ink composition.
 5. The photocurable ink composition according toclaim 1, wherein the ink composition is allowed to adhere to a recordingmedium and is cured by irradiation with light from an ultravioletlight-emitting diode having an emission peak wavelength in a range of350 to 420 nm.
 6. The photocurable ink composition according to claim 1,wherein the ink composition is curable by irradiation with an energy of300 mJ/cm² or less from an ultraviolet light-emitting diode having anemission peak wavelength in a range of 350 to 420 nm.
 7. Thephotocurable ink composition according to claim 1, wherein the vinylether group-containing (meth)acrylic esters are 2-(vinyloxyethoxy)ethylacrylate.
 8. An ink jet recording method comprising: allowing thephotocurable ink composition according to claim 1 to adhere to arecording medium; and curing the adhering ink composition by irradiationwith light from an ultraviolet light-emitting diode having an emissionpeak wavelength in a range of 350 to 420 nm.
 9. An ink jet recordingapparatus for allowing the photocurable ink composition according toclaim 1 to adhere to a recording medium and curing the adhering inkcomposition by irradiation with light from an ultraviolet light-emittingdiode having an emission peak wavelength in a range of 350 to 420 nm.10. The photocurable ink composition according to claim 1, wherein thecontent of the vinyl ether group containing (meth)acrylic esters is 10to 40% based on the total mass of the ink composition.